It's definitly not a cheap hobby to get into. I started out with 1/10 scale stadium truck about 4 years ago and I had an easy $1000 in everything I needed to race with. That includes the tools, truck with mods, tires, starter box, FM transmitter and receiver, and Nitro fuel (which is $30 a gallon now). 1/8 scale buggy was ALOT more $$$ to get started in but also alot more fun than 1/10 scale ST's because they are a shit load faster, they handle like they're on rails and they don't break nearly as much as a fragile 1/10 scale ST. Now I race both a T-Maxx and an E-Maxx monster trucks. Niether one are very expensive to pick up used and the parts can be bought dirt cheap on EBay.
If you want more info check out http://www.crcrc.com for indoor racing and http://www.cbrcr.com for the outdoor track in Grove City.