Nook HD is cheap nowdays.
Refurb'ed ipad minis are $279.99 now, I think.
There's a few $199 tablets that run android and are good. ASUS has one or two and they also make the Nexus 7, which is still a good tablet.
I believe Best Buy has the Samsung Tab 2 on sale this weekend for $200 and they throw in a case. Not top of the line, but a good price on good hardware.
Probably most important is that he's 9. He probably wants want all his friends have/want. You could throw down a cheaper, better tablet in front of him but if all his friends have a different type it's probably going to be nice, but not great.