You need to ring around and get quotes based on the business that you are looking to run. Too many variables to give you a general price.
However, to give you an idea, my insurance went from ~1500 odd in Portsmouth to ~3500 odd in London using the same company and info. I am 26, no points or claims, no restrictions engine size or insurance group (too many companies would be receptive, then balk at my group 20 Merc) and am operating from home with a 15k stock limit.