I was under the impression vasectomising a hob is actually a pretty tricky operation. As a result quite a few vets don't offer it. The last time I had a hob snipped I rang round about a dozen vets to get quotes and about half of them said they won't do it as it's too complicated.
I had one refuse to do it too but there are plenty who will. My advice would be to shop around, I was quoted anything from 60 quid right up to 130.00
Like you I had a range of quotes. From memory I think the cheapest was £73 but most expensive was about £180!
If you ever want one done drop it down to me mate I wi