I feel some are taking this a bit too seriously. It is all about the spirit of the event and hopefully a grand day out on old bikes. No set of rules is going to cover ever eventuality but they were brought in because people were riding the Italian version on modern mountain bikes and racers with suspension, carbon frames etc and this was starting to spoil the character and intention of the event.
Trying to get your modernish bike to fit the rules is, with respect, not what you should be spending your time doing. Go and buy an old steel racer from the 50s ,60s,70s and so long as the components are from the same era, you will comply immediately and with no trouble. There are plenty out there and not necessarily that expensive. After all, what is the name of this website ? If you are not interested in old bikes why are you here ?
As to cost, I am amazed it is so cheap ! I know I qualify for a £45 pre-booked/aged person but it includes 3 nights camping, some food, entertainment, event organisation, memorabilia etc. I can easily pay £15 a night just for my camper van so this seems good value.
Enter, Ride, Enjoy !