For years my thing is to get the most possible out of my car with the least amount of money. Even back in the day I was buying radio shack stick packs. I would disassemble them, wire them up with new tabs and direct solder to my speed control. I'll share some time sheets then at the bottom I'll tell you what I'm running. By the way I'm Robert. The other guys run some high dollar stuff. Tekin, and Orion speed controls, Reedy motors, D4's, 24k's
The first time sheet is actually 2wd open mod. That's right. I run my 17.5 car in both 17.5 and mod. Its a Losi 22 3.0 4-gear, I run Turnigy Nanotech ultimate batteries, Trackstar V2 17.5 motor, $28 trackstar sportsman speed control, trackstar 1256 titanium gear servo, like $30. I have it geared at 70/35 and have the timing at like 40-45 on the motor. The other time sheet is 4wd mod. Look at my 2wd time compared to the 2nd place 4wd car.
What I would do in your situation. Get something like a hobbywing, just stock or a xr10, one of those green eco motors, they are good. and spend the rest on gears, tires and track time. I'm sure whatever way you decide to go will be fine. Just wanted to share some of my thoughts and experience.