I would have to say the atari 2600 would be the most expensive system to try and complete.compared to the nes which has 6 or 7 games that command a high price theres easily 50 or more 2600 games that cost a small fortune.and for a system that came out so early there are tons of games for the system and it seems like theres a new homebrew game coming out all the time. as for the most expensive individual game I know air raid went for 3500.00 dollars but I think the nes gold competion cart as far as I know demands the highest price for a video game.