I like the idea od a Turbo'd or Supercharged Clio, but I don't like the idea of the price. I am not saying that companies overcharge for the kits (don't really care if they are or aren't, what I think won't change their price either way).
I added circa 100bhp to my last car (with the potential for a fair bit more) for less than 1k (prob about £800-£900), that was mainly because I did everything myself and found a decent priced donor car.
That conversion was easy because it was just basically an engine swap with some re-wiring, it's a shame there aren't any higher powered engines that would bolt into the Clio in the same way.