The top of the pathway for the leisure sailor, and the qualification charter companies and insurers recognise anywhere. Both grades are a preparation course followed by a practical examination with an RYA examiner.
Prep and exam together: £840 in summer, £780 in winter. Preparation alone, without the exam: £720 and £660. The RYA charges its own examination fee on top: £241 for Offshore, £208 for Coastal.
Note that preparation on its own carries no RYA course completion certificate: it is practice, not an award.
The sea time is the hard part, not the course. Offshore asks for 50 days at sea, 2,500 miles and five passages over 60 miles. Years of club cruising is how members get there.
Yachtmaster preparation runs on request rather than to a published calendar. Setting out this year's RYA courses, the Training Director asks anyone wanting a Yachtmaster prep to get in touch so that one can be arranged. That is the way in: say you are interested, and a course is built around the people who want it.