How much dose garages charge to fit a waterseal in a gilera vx 125?

my waterseal is gone in my gilera runner vx engine, and i have to idea how to fit a new 1, so i'm going to get a garage to fit it, but i really needa know how much they charge to fit 1? any1 have any idea? i thought i would be around �100-�150, but not sure.