A good undented not too rusty passenger Syncro should not run much
more than about $7500, stock. A Westy Syncro in good shape can still
pull $25K stock.

With that said there are some that will go for less. A few dents, a
bit of rust. Maybe trashed interiors....

I can't give an estimate on Dokas as they are just too rare for sale
in the US to have established a going price. But I paid $25K for my
Tristar Syncro. Non-Tristar Dokas should be less.

Now the cost of a Diesel conversion is going to depend on a lot of
things. Not the least of which is...are you going to do the work, or
pay someone else. Labor costs. The TDI's are still new enough that
their prices aren't cheap compared to other engine conversions. But
Karl Mullendore can give you the Overland price (since he's a
dealer). He runs a TDI in his Syncro Westy (on biodiesel too.)