Did you speak to John Williams at SOS? If you’re sure you want to run a Seagull then he will (has) be(een) able to advise you. John will quote a realistic, fair price for the work involved and he’ll take pride in doing a good job.
P.S. Having looked at John’s site it seems more than likely that you’ve spoken to him – I see a nice low hours Forty Plus for sale. I’ll leave this reply for anyone else who might be interested in Seagulls or perhaps Eventides – another of John’s passions.