Peak Imaging are cheaper for a single roll of black & white, process only, if you were so inclined. £5.88 with them, £5.95 with Ag. From what I gather from the posts, faster turnaround too.
Colour is cheaper with Ag though.
I was referring to Metro colour labs when I wrote that the turn round time was around ten days, I just sent my first C41 135 Kodak Ektar into Ag, and got it back from door to door in three days.