Hi Gary
you will probably want to make a spinner,
If you don't have much HW stuff about. the cost has got to be about £3-5K. for something that will do. and that's with you doing the work!
That's a lot of money for 1 possibly 2 events. with 2 fight each event (if things don't go well) that's about £1k per fight! there may be a continuation of this in future but there are no guarentees.
OK you might be invited to the USA for a show but there are plenty of teams that have been quietly developing their HW skills with newer tech for the last 10 years, that want to go as well.
I don't want to put you off but if you want to enter the HW scene I would advise some thinking before you are drawn into a costly and possibly disappointing experience.
How about making something that can go to the other events that happen in the UK. Lifter, axle bot, axe or ram bot. you might just find making a competitive (none flipper ) HW isn't as easy as it once was.