I had one large side window resealed at the same time as I had the floor in the doorway repaired ,(Water damage). Cost me £500 in total for the two jobs.I think the window was about £150 on its own as it was a two man job. Work was done in Chesterfield area.
I've done a couple.Depends on the type of window. Have a look on utube.Theres a guy on there who shows you how to do it.You dont have to be skilled to do it.Just take your time and pick a nice dry day to do it.