When we were anchored off Studland, a nudist diver popped up from the depths (all 3 metres) and asked my wife if she wanted her bottom scrubbed. I don't think she asked for his card!
Assuming your not the IRS, from memory between £30-40, for a scrub on a 40' TSDY & also check & replace anodes. Anodes provided by owner. He was down a long time - spent most of the day underneath.