You can always do the XKCD trick
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But even this seems to have gone stale over time, as retro game prices get sticker (even going up as vintage games come back into fashion).

One thing I don’t see on this list is “piracy”, which is a bit weird if your line is $15. I find a lot of bargain bin games to be as bad or worse than FTP games. $20-30 has historically been my sweet spot