Most of the main stage races are now considerably more than £500, particularly when you add travel in. Trans Wales is a lot more than just the trail centres, you get some fantastic riding in the middle of nowhere and a week with likeminded individuals. I did 2008 in the monsoon and said I’d never go back because the rest of the organisation wasn’t up to it, but I hear it has improved considerably since then.
Other cheap-ish option include two in Poland, one is the Trans Carpatia I think, and the Trans Alp isn’t that expensive but fills up very quickly.
Ones worth doing but cost lots more are Trans Provence and BC Bike Race (TP has incredible singletrack, and BC Bike Race is supposed to be much the same) or the Cape Epic – best organised event I’ve ever been to but difficult to get an entry.