Probably need to explain more what you mean by "bare bones."
If you really mean "bare bones", you wouldn't buy a pre-made microcontroller.
So do you want to build your own chassis, control system, servros, DC motors, and RC system? Seems like a good "step by step" guide would be looking up each of those and learning how to integrate.
...now, I can't find it - but buried somewhere in there is a build thread of this guy who created from the ground up, with (supposedly) little-to-no access to a machine shop (that is, he used mainly hand tools in his home) - a 4wd sand-rail like machine, that was fairly large (I think it was powered with a chain-saw engine).
At any rate - those kinds of threads (as well as build-up threads using commercial parts or kits) - will show you everything you need in order to build an R/C car; what I mean, is that it will give you an idea of the mechanics and pieces, and how they all fit together (and what you can build, vs what you'll have to purchase).
Building an "automobile" of any size isn't an easy task; they are quite complex machines (even 2-wheel drive). Good luck...