When you "say around 30 minutes", presumably you mean 30 minutes on site. But there's more to it than that isn't there?
First you ring and speak to a receptionist who has to be paid, in an office which has to be paid for on a telephone system which likewise, is not free.
The surveyor, who has studied for a number of years, and also needs to keep up to date with building regs etc, as well as issues which might be specific to the locality, then has to travel to and from the site (for which he has a right to be paid). If he comes by car, there are petrol and other consumables to take into account, as well as wear and tear on the vehicle.
He will also of course be paying premiums on his professional indemnity insurance.
Having visited the site, he will return to the office, and prepare a report on a computer (expense) which will then be printed (expense) and posted to you (expense).