Shenanigans don't get all down in the mouth before you start, this is certainly doable. If you want to do this on a local level find the association that races closest to you and as mentioned ask questions to figure out what class your 550 will run. Take pictures too to remind you of all the good ideas guys have! The race association will have scrutineers that can help answer questions about eligibility.
KOS nailed it, and there is no excuse anytime for an evil handling, poor braking, bad suspending motorcycle. If you want to race that's the starting point. Removing weight is part of this. You can easily draw up a budget from the info you gather. If you're so inclined and can do the work at least you'll save money there, but the words racing & cheap are mutually exclusive.
As was mentioned consider taking a school it'll fast track you to the fun. We all know here motorcycle people are the best, vintage racers are the best of the best!
I may well be the posterboy for how not to get involved, one thing has led to another and the bike's still not ready and I have a fair chunk of change in it.
I know better, damn it, I do know better. I didn't need to go sooo far building a bike to get started and original toyed with the idea of a TZ or even an RD and would have been racing by now but I'm drawn to these fours. I did take a school recently to aquire my race license and it has lit a fire under my ass.
Go for it.