You can buy one from Tokyo Marui. not very well known, nor is it preferred. But modding a springer into an electric gun defeats the point. The "Tokyo Marui Gindan Glock 26 (G26) Semi Auto Spring Airsoft Gun" Is one of these. See related links for more info.
The automatic/semi-automatic mechanisms work because as a round is fired, it uses the gas and recoil from the explosion to re-set the gun. Air soft pellets are just pieces of plastic, and do not have any propellant, so they need gas or batteries to cycle the gun.
Yes, all airsofts are legal in all states, but some states may not allow semi- auto machine Co2 airsofts
Yes, no or maybe are all correct answers depedning on how you intend to use the item. Spring airsoft guns use less parts and they don't need batteries (no need of charging), but they don't have auto/full auto capability. On the contrary, AEG's have those capability, but have more parts and need batteries to operate (hence, need more maintenance and, of course, more money to spend on it). Well, the choice is yours.
Not if its not designed that way.
No. it has to be cocked each time.
No. Spring must be cocked before each shot.
http://www.hobbytron.com/SpringUTGBlackS368BHSniperRifleLPSOFTS368BH.html
yes unless it runs on gas, but guns come with the spring
It means that each time you pull the trigger, a shot is fired. The other models are: spring/pump action, which need to be recocked after each shot, and automatic which will fire as long as the trigger is pulled.
There are too many types: airguns that are used in the auto industry, Air Rifles, Air pistols, Air soft guns.
It has to be electric (AEG).
I assume you are asking about BB guns not Air soft guns. There are a few that fall under $50 but they are C02 not spring powered. Marksman makes a line of spring pistols under $50 but they are terrible and not worth the cost. See the link below for C02 air guns.