George
If you don't have any luck getting a Yamaha turbo at a sensible price (and list price is frankly laughable) then you might want to consider getting a different turbo.
When my Yamaha (4 cylinder) turbo self destructed a few years ago I got a replacement from Universal Turbos
http://www.universal-turbos.com/
There are also other companies who particularly specialise in marine turbos who would be worth a look.
John