In Alabama local games shops ask $20 minimum for a beaten up DMG, PILs are upwards of $50.
I think the prices are reflective of a) the fact that times are exceptionally hard for game stores in my area b) lots of rich kids go to my college and are dumb enough to buy "cool" old stuff from these stores c) due to my part of the state being very low-income for decades, handheld games probably weren't that popular since they could be easily lost or stolen. Also, local vintage game stores are about 60 miles apart from each other, and take advantage of being the retro-game monopoly. They pay their staff to comb the thrift stores and pawn shops every day to nab anything cheap to flip at the store. I'm jealous of their strategy and I wish I could find a hole in it so I could get some deals.
I mostly buy online, once got a clear DMG, plain grey DMG, and a yellow Gameboy Color all perfectly working with battery covers and good screencovers for $15 with free shipping on ebay. Still rocking that clear DMG.