£250 is max. New preferred.
I bought my 15-85 from Simply Electronics - delivery was ok -around a week rather than the couple of days quoted - and price was very good at £499, £538 with a Hoya pro filter - less than most other places 'unboxed' versions split from kits
It's a great lens, but doesn't really help the OP
I'd go for the Sigma 17-70 - the non-OS model is cheaper, and supposed to be slightly better optically if you can live without stabilisation. I used one for quite a while and only upgraded to the Canon 15-85 (for the USM focusing and the 15mm wide end, rather than for improved image quality).