1: SOMEONE needs every part. It makes it tedious, but you can do what I do- search the "Machines" subcategory only.
2: Buy it Now is popular because they think they can get more for it. "A bird in the hand" and all that. In the end, someone might pay 40 bucks for a new Pac Man CPO if they can have a guarantee of owning it, and they probably wouldn't pay that much STARTING BID on an item... but since a lot of parts/machines are unpopular, starting a machine at 99c with no reserve and getting one bid means you're screwed. And reserves suck, so many of us don't even buy from auctions with a reserve price (it's all just a ploy to make it look like it costs less, when really, you would have to commit to an insanely above market price for an item)... in the end, Buy it Now is a good option, and Best Offer makes eBay a veritable CraigsList. If you would be happiest with 900 for a game, make that your BIN, and if nobody is willing to pay that and would rather risk being out-offered you can surf through the offers until one comes around you're willing to go with. I miss the days of auctions where you could be the only interested one in an area interested and win a working machine for 50 bucks... but in a world where 90% of auctions have a reserve price, usually around 2000 bucks for a broken conversion, BIN/BO is the best alternative.