tbavprof - I seriously doubt the setting of transition altitudes has anything to do with fee collection. The point of having 3,000 ft as the general transition alt in the UK (there are TMAs with different TAs) is that away from some areas of the Scottish highlands and a bit of Wales, there is no terrain hazard above that alt, thus at FL35 everyone is at least on the same altimeter setting. Altitudes should be used where terrain separation is an issue, but FLs are more appropriate when well above terrain and the issue is solely one of aircraft separation.
And to correct your erroneous post, flight levels in USA begin at the lowest available FL at least 1,000 ft above an altitude of 17,000 ft.