I've thought of getting the kit too! £25 each round here for whenever the weights come off or just swapping tyres between rims is a rip off. I could understand it if the fitters were hacked off because you were turning up with internet tyres to save a fortune and wanted them fitting, but they'll do the same even when the tyres you're swapping between rims were originally bought from them in the first place!
Amongst mates I know where I can borrow pretty much any tool, trailer, use of a 4poster, etc from (I can't even remember who's got my engine crane currently)... apart from tyre fitting and balancing. Don't know anyone that has got their own kit!