I race a V-One S. I just spent $670 on parts for it including the blue heatsink and special chassis, as well as a lot of spares. I bought it all from Radiomodels, they have some cheap prices there!
Some hobby stores are only out to suck money out of you, but my old one that closed down wouldn't sell me anything that wasn't necessary.
Just invest in the heatsink, maybe the special chassis and the adjustable aluminium shockers and go from there. Buy different colour springs and different shock oil weights. Also, go down to your track and practice a lot. All that practice will add up!
Also, ask the people in your class what they find to be useful/good on/for their cars.