Yup, what he said ^^^^
Join a club - club racing is great! You start off on ...... little 125s, then hot 125s, then 250s, then 600s, then - whatever.
It isn't anywhere near as expensive as people on here have made out.
I raced for 17 years on everything from proddy 250 through to BOTT and every form of racing from sprints, beach racing, hillclimb, enduro, trials, endurance, to desert hare-and-hounds multi-day events.
All through a bike club. All at a reasonable cost.
Obviously the faster you go, the more expensive it is... but it's a great hobby.
Now I am 'of an age' I am seriously considering going back to classic racing, but not the BSA/Matchless/Trident type, more the 250 strokers... cheap and fun, get a lot of events done in a year without it breaking the bank and the competition is fierce!
I know you posted it a while ago, but good luck