My vote goes to the Kindle Fire. I got a free Lenovo A7 with a laptop I picked up and gave it to my son. His aunt (same age) got a Kindle Fire, and hers screams in comparison. You can get them for a fair price too.
I got one for £30 a while back - battery absolutely sucks, but performance wise it's absolutely fine for the usual web browsing / facebook / email etc.
Sorry to be a grave digger. I've still been contemplating getting an Android Tablet, My Mother has the Hisense Sero 7 Pro Tablet which is a great little Tablet. I am giving it a try and see it goes.
Maybe you could look around for a first generation Nexus 7, I'll bet you could get one fairly reasonably. It's not the newest model, but still very good.