I just bought a 2nd hand car off eBay after a 10 year break and didn't want to spend too much. I'm in the process of getting it up and running. It came with loads of spare parts and tuning options. I had budgeted for the electronics, charger, batteries etc, but found I had to spend quite a bit more on small items. They were cheap in itself, but if you add them up, quite a bit comes together. This will be similar for a RTR I suspect. You'll probably want some different springs and oils, some tires. Just something to keep in mind.
Even though I still had a lot of rc gear, I found all the fixings had changed to metric: bunch of new tools. The car had a gear diff: needed different diff oils. I wanted a new body with my own colours on it: body + paint. The servo I had didn't fit: new servo. Replaced the ball cups and the spur. Needed a set of shims and some fixings were missing. All in all I spent 150-200 Pounds more than I had calculated up front on small items.
You can buy some good equipment from the sales section of forums here which will save you quite a bit.
I also did consider a RTR at first, but knowing myself I'd probably start upgrading it soon and end up spending more overall in the end.
Now I spent a bit more up front, but have the car I wanted sitting here and I don't think I'll feel the need to buy any further options, except the bits you wear out (tires, gears, some oils etc.) But we'll see how that goes
