Can't help but I can commiserate, Westerbeke prices are obscene. I needed a double groove pulley for the alternator and it was $540, single groove one was $70.
One possible route is to find out what block the engine was marinised from. It may be that you can find the oil pan at a tractor dealer or somewhere similar. My Westerbeke (W58) is the same as one of the Perkins and is also a Mitsubishi tractor engine. Unfortunately these tractors do not seem to have been sold in North America although they were common in England, but you need lots of time for shipping from there at reasonable cost. Worth the research time.
Heading back to Lake Ontario for this summer. Now in Bermuda and heading to Long Island Sound in the first week in May. Then on to the Hudson and the Erie Canal.