This site is great in providing answers to many of your r/c questions. Here is an alternate site than can talk to your r/c drag racing questions specifically:
What chassis do you have? That will help in making a recommendation. At the electric Pro Stock level chassis are available from entry to pro level.
Are you near a track where you can go hang out and watch the action? And ask around the pits? Have you entered a r/c drag racing event?
If you are new to the sport, here's my recommendation. Start slow and start in Bracket Class. Get some used stuff from your LHS. 19T brush motor, ESC and NiMh 6cell pack is a good start, and won't cost a lot. You can always step out of Bracket Class later to Pro Stock with your chassis by adding high-dollar components if you want to.
Make some passes down the track. See if you really like it. And, at the same time talk with the competitors there. Get a feel for what classes are runnning there and which components work best for those competing.
Welcome to the niche sport of r/c drag racing. Good luck.