I see auctions on GunBroker with people asking $200 for a single magazine. I wouldn't ever pay that much nor feel comfortable asking that much for a single magazine. I bought 7 magazines recently that are a bit older and am trying to determine a fair value.
2 are unmarked (i.e. caliber), Glock 17, baseplate shows Glock but no hole for baseplate removal tool. No part number on baseplate. U-notch.
3 are marked .45, Glock 21, baseplate shows Glock, 3941 with hole. U-notch.
2 are marked 10mm, Glock 20, baseplate shows Glock, 3941 with hole. U-notch.