steampowered.com.com has DF1 (USD-5.00 under) and most of the other as will under USD-10.00
direct download version of the game be install after they been downloaded into progame file/ steam (folder)
i think they will e-mail the key-code for the game to you asap! as soon it paid for too
really don't know reason i never got a paid game from them, but i read thats what they do. thinking of buy a game Bioshock 1 and 2 from them soon
maybe other who got a game from them can tell you how it all workout in the end
Delta Force: retail page for all
link:
http://store.steampowered.com/search/?term=Delta+Force
Details about steampower software browser link:
http://store.steampowered.com/about/
they all so have special deals on buying the whole serials as will. like in DF: 1-Extreme 2
i think it would be better then buying it from e-bay or any other reason it not use or chance of buying a game and key-code been banned/ lock