I can chime-in on the cost of inline 4 gas motors.  Dunno about the
little Fords, but the VW ones are plentiful for <$500, complete.  I have
one in my 84 semi-westie (no top) and it's given me about 50k trouble free
miles of travel with a fuel economy of 23-24mpg.  It has adequate power,
not like the Zetec, I guess, but with a 5-speed I rarely get slowed much
under the speed limit by hills/headwind combos..
  Don Hanson