There are loads of Zetec engined fords clogging up most dismantlers yards and there are always plenty on the 'bay. They're getting to be so cheap I wouldn't worry about checking it out just buy it, fit it, and if it blows up get another! you'd need to get through about dozen before tuning the CVH would come close in price. Sometimes even new crated zetecs come up - the last one went for £795 delivered.... A decent rebuild of the CVH will cost close to this and it's still only a CVH.
If your a fan of the CVH or just like a tuning challenge and have deep pockets then go ahead as such projects can be great fun ( the sort of thing I usually end up getting involved in) :0
But if you have deep pockets why would you be worried about the cost of a Zetec?
What ever you choose what's most important is to have fun
BV