Plenty of amps out there used for less than $1K if you're playing in a band. Contrary to popular belief Marshall and Mesa are not the end-all-be-all of amps. I've only played thru one Marshall I liked and they haven't made it for along time (original JCM-800, not the reissues). That model you will spend some $$$ on.
I've got a 50W Peavey 5150 combo (2x12") that used to blow the doors off of our other guitar players Marshall JCM900 1/2 stack. If you're playing anywhere that regularly hosts bands they will have a PA system you can plug direct into or run a mic from your speakers to. I think out of 6 years of doing gig's I only had to use the full volume out of the 5150 2-3 times, when the PA system went down.
Adveser is right about the vocals being amped. No guitar amp is going to do both, and it'll do vocals very poorly.
I've not looked at acoustic amps before, though, if that's your thing.