Massive rip off!
Here is who I use, and their price list. I'd even class these prices as premium! My local dry cleaners also does alterations and they are even cheaper.
The Zip Yard :: Clothing Alterations and Repairs
Try local dry cleaners.
I've just taken 2 pairs of chinos in, both are having 7 buttons swapped each, plus both taking in at the waist and they were only £22 each.