Hi Peter V,
Your local garage are ripping you off, unless there are other factors that they have not told you or you are not passing on.
So that other readers are not scared or put off the other info/quotes above are not too far off the mark – you can ‘Google’ and info on other websites will also confirm that.
I had mine replaced when the van was 6 years old ( from memory about £250 extra on service charge) and I know that costs have risen substantially since then and it will be done again early next year at 12 years. The recommended belt change interval is about 5 years , but this varies according to source. It’s a risky and costly business not to change them!
Fred