You could well be low on that estimate. Say I buy only 2 sets of foam tires, that's $60.00 or more in tires alone. Trued down to race specs they don't have much life and that assumes I don't need more because I chunked one. Add in the $20-$40.00 entry fee, and factor in say at least $1,000.00 worth of equipment depreciation over a period of say one or two years. I base this on have $2,000 or more worth of equipment which over a period of 2-3 years most of which is eithe worthless or 1/4 to 1/3 of its original cost. Then there's the other sundry items you just use up like motor spray at $9.00 a can, brushes, broken parts, shock oil, wires connectors, heat shrink, tape, glue, velcro, that motor you fubar'd, the replacement body. And there is likely more.
If touring car is the spec class, you can expect to spend a fair bit to run with the pack.