If you are mechanically inclined, do the work yourself. Check out my engine rebuild and related maintenance site: http://j30rhapsody348.blogspot.com/p/rhapsody-j30-348-yanmar-2gm-rebuild.html

Parts are readily available for the engine. The one time investment in the Yanmar service manual is worth its weight in gold. Electrical work with harnesses and connectors is fairly simple, assuming you are not trying to manually reterminate old connector plugs on a harness. The generic Yanmar schematics are accurate and easy to read.

If you can negotiate with the seller on some of the items needed to be done, it may help defray the bill.