Most all buy their way into this sport. Only a few drivers are actually paid to drive. Even the top TT drivers own their truck and program. Some have sponsors that foot all the bills most don’t. Good drivers usually start racing in limited classes and move up as they progress.
Don’t build anything! Buy a 1600, class 9, class 2000 truck. Then get a group of friends and go to a race or two. try to link up with a team to understand pitting. Then prep your ride, test, race, repeat. Don’t get stuck on racing the big series. Smaller series help support each other more. I pit with 2 other teams.