I got a charbroil grill with 47KBTU I think. It does a nice job. All you really need is rotisserie capability, which they all seem to have. Don't go too underpowered. I think Ron (Kyle) recommends 30KBTU + ....more power lets you make changes quicker, which can be useful. Some people scrounge thrift stores, garage sales, etc and you can get a grill for next to nothing.
I wimped out and bought the motor straight from him, but you could definitely get one on ebay cheaper. But then you'll need to mount it. Sort of a money vs. convenience tradeoff.
It is pretty much a turnkey operation. I had to drill a couple holes to attach my motor to the side ledge, but that was about it. The drum is the heart of the operation.
Highly recommended.