i bought my converted shell off ebay, only cost me 200 pounds and its really solid. Loads and loads of work on her but i think it'll be worth it

If you sniff around they are there to be had, mine is a mk2 and i have seen a couple of them about. Mk3s are more of a problem as the wheel base needs extending to get any sort of handling. A guy round the corner from me has a rwd mk3 with the front wheels brought forward 1 inch.

If i was you i would try and get one converted for mk2 escort running rather than cossie. Just my opinion really and i have no idea which is "better" but mk2 escorts have a lot of rally designed parts readily available.