Great car, good price. They command less than the diesel because of the MPG. But if you can stomach the costs (low to mid 20s) they're an excellent car. As good as the ST is, the Mk4 is a better all-rounder. The VRS is a great car too but (although i'm biased) the Mondeo would get my vote.

As it's a Focus ST engine, you can do pretty much the same mods and get plenty of power out of them.