i have been rallying since i was about 13.
Join a car club as others have said and go from there.
If the car is a stage spec car then you won’t be able to take it on “enduros” etc without putting interior back in it and it may be over specced as enduro rules are much tighter than class rules for stage rallying.
I have a tarmac spec stage vw polo, that’s currently getting rebuilt. Single venue tarmac rallying is relatively cheap – entries from as little as £130 and alot less hard on the car compared to the woods.
you’ll need a co-driver – we used to split the cost between us, co-driver pays entry and buys pace notes (if required) i would supply fuel, tyres etc etc for the running of the car. normally works out about the same.
You’ll need to go to do a BARS test at a rally school to get the license (national B Stage)
you could also look at gravel sprints, but there are alot less events and you need a gravel spec/forest spec car, which generally needs more maintenance