I also think that you will be more competitive in 1/10 scale Gas truck racing than 1/8 scale since alot of the racing guys probably will have a race quality buggy and race quality engines, and the prices on those are really out there compared to the RTR buggies.
you could also consider 1/8 scale monster truck if the class is there to run, and it would be a fun basher.
If your new to the sport go with the 10th scale they are alot easyer to work on and then when you get more devoted into the hobbie and you know what your doing go with a OFNA 8th scale buggie. My first truck is a Team Associated RC10GT rtr plus. They are like $269 on tower hobbies. You can pretty much do every thing with that truck, plus they are really durable.