Well while it's not all about 1/4 mile performace I'd still take an ST over a mustang (in part if I'm going to buy a Mustang it has to be V8 powered one) since the driving dynamic is different and the Focus has a little more utility but on the other side I can get a nicely equipped WRX for the same price range as an ST and I get AWD and it has a nicely proven aftermarket when it comes to mods.
And like you stated with the MS3 and you have the Genesis coupe in that competitive price range also.
It's a buyers market when it comes to sub $30k perfromance cars so it's a win-win all around and is good for the sporty car market as we're seeing even more cheap performance cars coming out every year.
'12 Focus Red Candy SE Sport 5 spd
'99 Toyota 4Runner Sport
'11 Subaru WRX STI Hatch