Expenses
It is reasonable for the beekeeper to be reimburst the travel expense of attending to a swarm, and should this be mentioned before arrival then at least you would have been forwarned. Some county associations such as Essex do charge so be sure before you make an agreement!
Some beekeepers will collect a swarm because they want the bees to add to their own stocks. But while the bees are being collected a nice cup of tea will rarely be declined.
As a suggestion this mileage rate is used by Warwick University and might help as a guide. (40p per mile)