I don't know if it's that cost-effective, as the exhaust/inlet are the opposite way around to the Zetec engine found in the Fiesta's... also you'll have to get custom engine mounts made up!

Get a 1.6 Zetec-SE engine from the Zetec-S, that produces 103bhp as standard, but with cams, exhaust, manifold, sports cat and a remap you'll easily see 150bhp - all that will come to around 1500 (not including the engine!!!)

TB's will get you passed 170bhp (possibly) but will require a bit more money to get there... and aftermarket management (megasquirt, omex)

If you want a turbocharged engine, then look into the CVH route as a few people have now fitted these into their ZS, and will essentially be exactly the same fit in the mk4!!

HTH