I am not really sure but Ramos 970 should work well with SDK. It's a bit expensive, but maybe there are some cheap clones on a market. Just search the internet.
Another thing is that, I have a cheap RK27XX player:
8GB 3 16:9 QVGA MP3 MP4 MP5 Player FQ5-8R [MP4] - $45.97 : TinyDeal Direct Online Store, MP4/MP3 Player, Mobile Phone, Memory Card, Accessories
But SDK doesn't work very well with this player, but I am working on making it compatible with it, so if you are not in a rush, you can wait until compatibility problems go away, and then buy such a player. It's only $45 with free shipping to whereever you want.