I... asked for the promo stuff. Yep, just walk up and ask. You would be suprised. Once they're done with them, the stores just throw them out. If you're lucky, you will find someone who doesn't like to waste stuff (such as I've found).
Believe it or not, I *really* haven't spent that much money on the games you've seen. I don't buy games off of Ebay. I don't buy every game at full price. I've got some tips.
1. If you're going for complete collections, or collecting in volume, build up cash for stuff like $5 Circuit City super clearance sales. See all those Gamecube games? 40 of them were bought for $5 at Circuit City. Toys 'R Us has the green tag sales, and sometimes good stuff slips through the cracks. I bought Devil May Cry for $1 last year, plus a handful of GBA games.
2. Garage Sales and Nickle Ads. Go through them. If you go to a garage sale and they don't have any games out, suck it up and ask the person running it "Do you have any Nintendo stuff?" Garage Sale people love to make sales, and they might just pull out one from a closet or something and sell it to you. Plus, visit your Goodwills and various other junk stores. Go to pawn shops.