For the great scrounger I think that the I-4 route is definitely the
cheapest.  I think the best bang for the buck, however, is a 2.2L or 3.3L
Subaru.  A do-it-yourselfer can do a 2.2L for about 2K and a 3.3 for 3K.
The 2.2 puts out 135 HP and 130 ft lbs of torque and the 3.3 puts out 230
HP.  The 2.2 Subaru gets about the same mileage as a I-4 but with a
significantly more power and is a whole bunch smoother.  It also fits under
the lid. The 3.3 gets about the same mileage as a WBX (a little worse around
town)  but makes the vanagon a whole different animal.
      For the average do it yourselfer I don't think there is much cost
difference between a Subaru and an I-4.  Yeah, I know a few people have
gotten smokin' deals on VW diesel parts, but they are not that easy to find.
 Subarus are a dime a dozen.
      For what it is worth, I have seen used Subaru conversion parts show up
pretty cheap also.  It just depends on how patient you are.
      I know turning a German car into a rice-burner is a henious crime to
some, but I sure like my Westy a whole bunch more that I used to with a WBX.
 I have driven a couple of I-4 swaps, and I prefer the Subaru.  Just my opinion.

      John
      87 Westy SVX-powered