Kindle Fire is one of the cheapest good quality tablets you can buy, specially a little older ones like Kindle Fire 2. The only issue with Kindle Fire is that it doesnt support Google play which has more apps then kindle app stores.
So If you willing to take some risk, you can try and root the device and add google play. Just follow this 2 links on xda developer forum and you will be able to the needful:
1. Root the kindle : http://forum.xda-developers.com/showthread.php?t=2074565
2. Add google play store: http://forum.xda-developers.com/showthread.php?t=2365224
I have personally used this root a kindle so it works. Try out if you want to for educational purposes.