Nuclear Weapons

This is too complicated to answer as written. First what do you mean by "hit"?

The effect wold depend on several variables, some of which are:

• yield
• burst height/depth
• burst slant range
• etc.

For a subsurface burst nearby at medium to large yield, even highly reinforced concrete buildings would collapse. Such bursts were designed to destroy underground missile silos, which are about as blast resistant as possible.

Airbursts, even of very high yield directly above a reinforced concrete building are likely to do little damage.

• Special Nuclear Materials (Uranium and/or Plutonium)
• Protective Coating for Special Nuclear Materials to prevent oxidation (Nickel)
• Fusion Fuels (Deuterium and/or Tritium or Lithium-Deuteride)
• Conventional Explosives (PBX, TATB, IMX, etc.)
• Exploding Wire Detonators (Metal Wire and fast Conventional Explosive)
• Dense Tamper (Depleted Uranium, Lead, Tungsten, etc.)
• Pusher (Aluminum)
• Fillers (Felt, Styrofoam, Honeycomb-Cardboard, etc.)
• Neutron Reflector (Beryllium)
• Electronics (Copper wire, Teflon insulation, Silicon chips, Fiberglass-Epoxy boards, Gold, Aluminum, Ceramics, etc.)
• Electronic High-Voltage Ion Accelerator Neutron Source (Tritium, Metal, and Glass)
• Casing (Steel, Duralumin, Aluminum, etc.)
• etc., etc.

Probably on the order of $100,000 and most are likely less. The majority of the cost is the high purity nuclear materials.

There are several major costs in building a nuclear bomb, which can be categorized as such:

Weapon Design: the scientific and engineering effort required to fully understand how a nuclear weapon works and make a functional design. This includes a significant amount of computer hardware to do simulation, a moderate number of highly-trained physicists, and a larger number of engineers and technicians to build and test various components. A conservative estimate to design a very basic, reliable "gun-type" Uranium bomb would be many tens of million dollars. A plutonium implosion bomb likely would require several hundreds of millions, with a "boosted" advanced atomic bomb design being slightly more expensive. A reliable hydrogen bomb design would almost certainly costs tens of billions of dollars, as they are incredible complex devices.

Fuel Costs: acquiring the atomic fuel (weapons-grade u-235 or pu-239) is astronomically difficult. Theoretically, it might be purchasable on the black market, for $10-50 million PER BOMB, but that's assuming you can find it (and don't get caught by one of the big country's spy networks). Making it costs tens of billions, as obtaining the raw materials isn't simple; you would need 100x the bomb fuel's weight in reactor fuel, or 10,000x the amount in raw uranium ore to start with, and the purifying plant is a huge complex filled with expensive equipment, and requires an enormous amount of electricity to run. Tritium/deuterium production is slightly less expensive, but not that much cheaper.

Bomb construction: making the actual bomb from a solid design is modestly expensive, as you need high-quality machine tools able to produce the parts to a very high level of tolerance. Overall, through, it should not be that expensive, perhaps a few million dollars to buy the machine tools and parts.

Thus, if you want to make multiple nuclear bombs, and have a reliable design that will work 99% of the time, then you probably need to spend $50 billion or so to make a simple A-bomb, $60 billion for an advanced A-bomb, and $200 billion or more for a H-bomb. After that, each bomb should run several million dollars each to make, regardless of type.

"Terrorist"-level bomb-making:

If all you want to do is build a crude, gun-type Uranium-fueled atomic weapon, that has a reasonable chance of working, then, assuming you have enough weapons-grade uranium on-hand, you can probably build one for a few tens of thousands of dollars, provided you can order certain machined parts from suppliers, make the rest yourself at a local quality tool-and-die shop, and have access to a few dozen cheap PC computers. I'd say you could easily build one for $100,000 or less. I'd give your bomb less than a 50% chance of working properly, though.

There is no ability to "home-make" anything other than a crude gun-type Uranium bomb. The design and construction requirements for an implosion devices require the resources of a large-sized company, at the very least, and such weapons will not work unless there is significant effort put into the design (you can't cut corners on the design or components of an implosion device, unlike a gun-type device). That is, even if I gave you 30 pounds of weapons-grade Plutonium, you'd still need 10-20 million dollars to produce an implosion device that might work (and, I'd give it a low-probability of functioning properly).

Hydrogen bomb design and manufacturing is impossible for anything outside a major government-level effort.

fission or fusion? oh well lets do both...

fission:

1. electronic fusing system sends timed electrical pulses to detonators
2. detonators trigger conventional explosive lenses
3. explosive lenses focus detonation wave into spherical implosion wave
4. spherical implosion wave hits depleted uranium tamper compressing it
5. spherical implosion wave hits fissile core compressing it
6. when fissile core reaches optimal supercritical state, electronic fusing system sends timed electrical pulse to accelerator fusion neutron generator to spray core with neutrons starting fission
7. within 1 microsecond fission completes, core and tamper have vaporized
8. inertia of the tamper vapor holds back the core vapor for a couple more microseconds, building up pressure
9. the bomb explodes

fusion:

1. fission bomb trigger explodes
2. x-rays from fission bomb are channeled around fusion stage
3. x-rays ablate depleted uranium tamper of fusion stage compressing fusion stage
4. compression of fusion stage compresses plutonium "sparkplug" rod down center of fusion stage
5. neutrons from fission bomb trigger initiate fission in "sparkplug"
6. neutrons from "sparkplug" convert lithium in lithium deutride to tritium
7. deuterium-tritium mixture is compressed and heated between imploding depleted uranium tamper and exploding plutonium "sparkplug" until fusion burn begins
8. high energy fusion neutrons trigger fission of depleted uranium tamper (providing about 90% of yield and most of fallout)
9. the bomb explodes

You can add as many fusion stages as you need to get the yield you want.

Richard Rhodes: "The Making of the Atomic Bomb" & "Dark Sun"

Without going into rigorous scientific detail, an atomic bomb works by nuclear fission. That is large atoms, namely uranium or plutonium, are split into smaller atoms in an uncontrolled chain reaction. One atom splits, neutrons from that split strike and split more atoms, which release more neutrons when they split which then split still more atoms. This releases a tremendous amount of energy all at once. Thus a single bomb, weighing no more than a few hundred or thousand pounds, explodes with the force of tens of thousands or hundreds of thousands of tons of TNT.

When we look at a hydrogen bomb, which is also a type of atomic bomb, we see that it works by nuclear fusion. That is small atoms, namely hydrogen, are fused together to make atoms of helium. This releases even more energy. Thus a hydrogen bomb has a force of hundreds of thousands, or even many millions of tons of TNT. Fusion requires fantastic temeratures and pressures to occur. The only way to create those conditions is to set off one or more atomic fission bombs. Essentially, a hydrogen bomb is a nuclear fusion device that requires an fission bomb as a detonator.

For the more detailed technical answer, use the link you'll find below to the related question.