I bought one of the Harbor Freight large buffer on sale for about 35 or 40 bucks. I think its a 7 inch wheel. It works fine for me, I only use once per year or so.
Like the others said, get a high quality wool bonnet / pad, will be around 30 to 40 bucks.
I have a friend who does details on the side and he uses a harbor freight buffer. However, I think he is on his second one. He details mostly 20 ft to 24 ft wake boats, but he also buffed a 35 ft cruiser last year too.... he says the buffer from HF is fine.
One note, we both prefer the buffer with the straight to the side handle. not the small wrap around loop handle.
My friend who details taught me how to buff. its not difficult, just takes some time to learn the finesse and feel. main tip is don't press too hard, and start at a lower speed RPM.