I just bought a Losi 8T roller from Nitrohouse for $329 and I am in the process of a similar setup, I had a 1515 2.5d and a Flightpower 6s 5000 pack laying around. So far I am really impressed with the truggy....its lighter and a lower CG than my 10s Revo
If I were you I would just go with the Castle MMM combo. Get teh 2200kv motor so you can run the 6s through it. They go for about $280-300 for the ESC and Motor. The motors are co-made by Neu so they are great quality. www.holmeshobbies.com has them for around $280 and he ships quick!
The Monster has them right HERE also $280 and by far the fastest shipping.