Best or cheapest? They're not the same.

Cheapest is to get a 2.0l Focus engine with ALL its ancillaries and engine mount, 1.8 flywheel & clutch, PCM, engine management harnesses, radiator, fans, all 2.0/1.8 hoses.

Best - same as above but add gearbox, cables and gearlever, driveshafts, gearboxmounts.

Unless there is a very good reason, a really cheap solution is to buy a 2.0 2001 Focus. If you have extensive body mods, swap that both ways and resell. You could even get a Cat C or B one as a donor.

Martin