I'd happily pay GBP 30 or so for a good strap -- I am reluctant to buy a strap that I can't actually see and touch, though. Some straps I just don't get on with, but worse than that, sometimes a picture of a strap looks nice, and the price promises quality, but then it doesn't turn out so well.
I have a fairly decent cloth-faced leather strap by Main Strap (or something like that) that works well for the guitar, but I had another one like it for the bass that I eventually wore out! After a little searching, I found a reasonably decent strap from Levy -- but it could be better.
Last time I was in Colombia, I went looking for guitar straps since there's a lot of good (and, by UK standards, cheap!) leather-work available, but unfortunately all the guitar straps I found easily were horrible synthetic weave and cheezy plastic snaps -- and marked up from the import duties! Bah! Someday, I'll get some leatherworking guy in a flea market to custom do me some :)