yes, in general, the zetec parts are cheaper. the zetec really platform has been nearly perfected including going through quaife for the dogbox if you want to. don't get me wrong, other foci are good too. just that the svt and zetec platforms are proven in rally, i've yet to see a dura rally car. the dura has more potential for power, but the winner of 2wd rally events are stock zetec foci. cheap, reliable and plenty of power. in rally, in fwd, you don't need 200 whp NA, svt will get you in plenty of trouble and it alread has the brakes.
terminator v8 in an SVT focus (soon to be boosted @ 20 PSI with a 2.9 L Kenne Belle on Corn!!!
(750 rwp and low 10 second focus, here I come!)