You may get a quote for the inspection, based on 30-40 hrs work say, but they can't quote on any remedial work until they've done the inspection. Some tasks, like replacing cables, batteries etc may have 'standard' times, but generally it'll be charged at actual hours after work has been bone.
When you do get a quote, it won't usually include extras like radio annual, flight test, CAA charges, VAT, Oil/filters/sundries etc.
Rule 22 - It will always take longer and cost more - even when you take rule 22 into account.