The rtr is for a starter. I don't know what radio system comes with the Yok, But most are just plain radio equiptment.
If you decide to go for the kit and then buy parts, it is going to cost you more. But you will have a better set-up in the end.
Motor (if needed costs $120)
Transmitter and reciever ($100 for a decent one JR-XR2)
two servos (plan for $75 a piece) Fast transit time .12/sec and torque of 50in.lbs. or more.
So you can see it starts to add up quickly. So being you are on a budget the rtr is a good way to start. Then add on as you want to. This way you have a running car to start with.
I have an RS4 with $600+ into it before I knew it, and that is without all the pretty aluminum parts.
Before you buy I would suggest buying an RC mag because it will have alot of add's for price comparsion. So you know what you can get into. And maybe save a few bucks too buying online.
Hope this helps ya