In reference to an RTR - I have heard a lot of great things about the OFNA/Hobao Hyper 7, they can be had for around $300 brand new.
I do however agree that a used quality kit would be a better option. They have tons of support and a great deal of information could be found on them here on the forums.
Personally I have a Mugen MBX7r which i'm planning to sell in order to pay for school. If you're interested don't hesitate to message me.