If you are interested in a truly obscure and quite rare handheld console of the first Gameboy era, well, the Bitcorp Gamate is a must buy, despite the fact that it usually sells for more than 75$, 60 euros or 50 pounds. The Gamate you see went largely unnoticed, sported mostly dire games and only got one positive review ever, meaning it quite possibly is the rarest cheap handheld ever produced. You can find out more about it here and here.
To grab one, well, do try your luck at this BitCorp Gamate auction at eBay. Seller ships worldwide and seems to be offering a well-preserved and fully working console, complete with three games: Galaxy Invaders, Monster Pitfall and Money Maze. Nice.