First find out what sanctioning body your racing under NKA or AKRA... different engine packages per. If your wanting to do this on the cheap... buy a short block off of Box Stock Project with an EV6 ,CL3 or BSP4 cam in it whichever rule set you need to abide by. Buy a good cylinder head set up for your rule set off of one of the many engine guys on here. Put a cheap PVL flywheel on it and a good plate carb and header and go have fun. All toll I believe you can have a new engine that will let you compete and have fun for about 400 bucks.
I’d go EV6 cam if it’s a bigger track and BSP4 if it’s a small bullring. In reality tho either will do the trick in purple to get your feet wet. Get ahold of Dover power and get a good ported head and purple plate carb and enjoy!