upgrading parts

[wilkinsi]

i'm looking to get a new guitar, but want to almost immediately replace the pickups and possibly the tremolo aswell. i can usually get the parts but can't be doing with the hassle of fitting them. does anyone have a guideline as to how much it should cost me to have the work done so that i don't get ripped off? bear in mind i live in the uk so economics will be different from the usa.