Welcome to the site Joe.
It all depends on the track you're at. In WI, pit passes are usually $25, and it's $250 to win at regular shows, but that will vary from track to track, and series to series.
We also have a points fund in our series here.
Depending on the cut of your tires, and how fast you want to go, I know people that put tires on every 3 races, and some that will go 8-10 races on a set