I'm with Wavey on this one. If you want to get into rallying cheaply, buy a second hand car, but budget for a few repairs.
The rest depends on your priorities. If you like the idea of spending time working in the shed on a project, then go nuts.

If you like the idea of getting out there and learning how to drive, then just get out there. Don't waste 2 years getting the car perfect, just get out there and do some skids.