Tales from the back of the pack in Club Ford.... Data doesn't have to be expensive.
If you are just starting out you don't need to spend big money for useful data.
Three years ago, I bought a used AIM Mychron4 gokart kit with GPS antenna for about $400. I got the coil wire wrap rpm pickup to work by taking twice the number of turns on the rpm signal wire to get a good rpm signal. The Mychron didn't fit my steering wheel very well, so I mounted it as a datalogger only. I continued to use the dash gauges to drive the car. The RPM and GPS data was very useful, including using the data overlay on video with my ContourHD camera. I spent $35 for RaceRender video/data overlay software and it works excellent.
The data I got was very useful. It showed me I exactly where was overslowing the car and losing way too much momentum and that more "go pedal" was needed.

I'm still working on that. The video overlay with data also showed where I did not hit my marks

and where I did. I'm still DFL, but working to get better.
Today, you can simply go out and buy an Aim Solo for the same money and get a significant amount of data in a very simple package. Very easy install, data download and data presentation for the new driver. When you want to move up, you sell it and reinvest in some good used equipment.
Recently I bought a used EVO4 kit, Mychron 3gold dash from Joe Cooley. Veracity racing data sold me their magnetic crank sensing RPM pickup for a good RPM signal. I added some used displacement sensors found on ebay. When done, I will have steering, brake and throttle data for very reasonable money.