When the Taito Egret Mini II launched, it took a somewhat different approach to rival mini-arcade consoles like the Neo Geo Mini and Astro City Mini.
While it comes pre-loaded with games, it also has an SD card slot which allows you to load up more titles. So far, two volumes have been released, and it seems that the production run for each was quite low, as copies are now changing hands for stupid amounts of cash online.
Volume 1, which includes Great Swordsman (1984), Ohgon No Siro/Great Gurianos/Gladiator (1986), Slap Fight/Alcon (1986), Daisenpuu/Twin Hawk (1989), PuLiRuLa (1991), Grid Seeker: Project Storm Hammer (1992), Riding Fight (1992), Light Bringer/Dungeon Magic (1993), Gekirindan (1995) and Cleopatra Fortune (1996) is being sold for well over $100, but it's Volume 2 which is going for stupid money.
The pack includes Night Striker (1989), Return of the Invaders (1985), Crime City (1989), Cloud Master/Chuka Taisen (1988), Wardner/Pyros (1987), Twin Cobra 2 (1995), Thundercade/Twin Formation (1987), Wyvern F-0 (1985), Operation Wolf (1987) and Yūyu no Quiz de Go! Go! (1990), and is selling for $500 on eBay. That's a confirmed sale, not just a listing – although another seller is asking over $600 for the game.
What makes all of this even more ridiculous is that this is literally an SD card with ROMs on it; it's not a cartridge or proprietary format. Surely it's possible to make more of these and ensure that people who actually want to play these games legally have the option to?
Volume 3 has already been confirmed, and launches this December. If you don't want to have to pay through the nose to get it later on, you might want to consider pre-ordering from a Japanese retailer as soon as possible.