I just put together a buggy and I went with the Losi. I know you don't want one, but it made the most sense to me since I own a Losi Ten-T and Losi is the most popular brand at my track (and I can get any part by the next day.) If you don't want a Losi don't go this route, there are lots of great buggies to choose from.
I went with the Clockwork modified JLR .21 engine.