If you like your classical, keep it! Go to a guitar shop, have a play on some steel-strings, and see (a) whether you like the sound at all, and (b) whether you like any in your price-range. And to increase the volume and attack of your notes, make sure you get your fingernails in on the act - the typical soft-guitar-playing problem is with just using the pads of your fingers to pick instead of the nails as well.

On the blues-on-classical-guitar front, I submit Davey Graham.

Slide-wise, I'm currently practising on an old 3/4 classical until I can afford a Dobro. It's not great (the action's way too low), but it's good enough for home use.

Grab.