Well according to stock class "rules" it is supposed to be the lowest cost class to race in. In general Autocross is supposed to be the lowest cost form of racing but go check out the guys that trophy and win at nationals in the stock classes, they by far are not spending minimally
But the classes are setup to build one on top of the other and you can work on your driving of your car as you progress up to the more “pre-pared” classes. Ever since I have started autocrossing, I have told anyone thinking about getting into it to run your car bone stock first. So I think you would definitely benefit from, essentially starting over and building your skills from the ground up.
"I have made a bar graph of my favorite Pies and I made a pie chart of my favorite Bars" - Marshall Eriksen