don't mess about with a kit car, unless it is for that rustproff fiberglass. If you look at autotrader.co.uk you can find mini and coopers for 400-on. i found a 1991 cooper with a 1000CC engine and an MOT, GREAT you can drive and repair for only pounds 650. If you must have a kit look at Paul Banham conversions (www.banmoco.co.uk) they do a roadster conversion don't know know what it entails!
just found this and thought of you!! Two to Four engineering does a mini like kit but with speed as the main idea!! can contact them via twotofour@aol.com. Another company that also does a mini kit www.framini.com or www.fraengineering.co.uk but I know nothing about them, minis are not my bag baby.