Neil and OP..

  My "already done" 84 conversion was $3000 complete, drive away two years
ago.
   Last summer when I was at my local German Auto parts salvage yard (in
Boring, Or) there were 3 complete 1.8liter inline VW motors for under $600
each..Everything included..The yard has a very good rep as honest.
There is a VW Cabriolet for sale here nearby for $1000, said to run
well..Too nice to jerk the motor out of, but Rabbits are plentiful
everywhere...the cars, not the animal..
   Exhaust?  Your local muffler shop can lash one up, in the van, on the
1.8liter, in probably 20 minutes..
  I've seen "conversion kits" for the inline 4 listed on The Samba for
around $5-800 bucks..Dunno bout those, but you need some factory-type bars
to carry the diesel-type block and a pan from the diesel and an adapter to
bolt it on the tranny..
  I'd say under $3k is pretty feasible (and that would include big margin
for un-anticipated costs)..If you are lucky, you might find a good one
!done! for $3k  like I did..
  Don Hanson

A "DIY" VW gas I4 for less than $3000? Possibly. Especially if one
hears/sees it running first. (i.e. no hidden costs to get it running)

Running donor: less than $1000?
DV parts ~ 700 - 1000?
1.8 head + Digifant stuff $?
Exhaust ?

Neil.