You can buy it at Wal-Mart, Game Stop, you can rent it at places like Movie Gallery or Blockbuster. Any game stores is where you can get if from.
Buy him from eBay
Not much. You will only hear it in Firefight.
300,000 credits
A company named "Lego" has a Master Chief Halo figure listed on Amazon at the moment (March 2011) http://www.amazon.com/HALO-Master-Chief-Navy-Blue/dp/B001L18CK2 This may not be an official Lego product. However, it will interchange with Lego pieces. It is a complete figure. If you wish to make your own, BrickForge makes custom armor, BrickArms the guns. This is most likely where the parts for the "Lego" product above come from. It would be cheaper to buy the pieces and make your own, especially if you want more than one. Kubricks also has parts that interchange with Lego, including a Master Chief from Halo figure.
Go to brickforge (see related link below) and they have "space marines" (spartans) in many colors and go to brickarmsfor some halo guns(assault rifle and magnum) and try saber scorpion for other armor permutations and weapons
Buy halo reacj armor in the startup menu in the armory for credits in online games
maybe ask them
there is no permanent cheats in halo 3. you need to unlock them by achievments. and, you can not get the flaming armor effect, it is only for bungie employees. in halo reach, buy the legendary package to get that armor effect.
you buy it and you can unlock some by halo waypoint (free download)
To unlock Recon armor in Halo 3, you originally had to beat all of the VidMaster achievments, but the armor is now available to all players. To unlock the recon armor in Halo: Reach you had to pre-order the game and you would get a long (25 character) code for the recon armor DLC. To unlock the recon armor in Halo 4, you had to either pre-order the game or simply buy the armor with your in-game credits.
Buy legendary edition, it has codes for it.
I would buy Halo if you have not already played it however if you just want it to see games you've already beat in better graphics I do not believe that is a good idea and would go battle field both are strong games but I personally am a bigger fan of the halo franchise