I'm your man for budget sound. I have been using two 15" Kustom passive monitors as my speakers for a jazz gig. We do have vocals now and then, and for talking, and its mostly crowds of less than 200 in restaurants, corporate settings and malls. If its's a music festival we have a sound man usually that the organizer provided for us. Crap shoot-ola on that one.
Anyway, back to budget sound.
I have been using the 2 15" Kustom monitors as Mains
I use a Crown 250 amp
http://www.amazon.com/Crown-NXLS1500-0-US-Power-Amplifier/dp/B003HZV2JS/ref=sr_1_2?ie=UTF8&qid=1419560486&sr=8-2&keywords=Crown amplifier
and a Behringer Mixer.
http://www.amazon.com/Behringer-X1832USB-BEHRINGER-XENYX/dp/B0036E8DE2/ref=sr_1_12?ie=UTF8&qid=1419560527&sr=8-12&keywords=Behringer mixer
All of the cats I know in this town use that Behringer mixer (3 different bands) so I didn't even think about it and just bought it It does the job.
The only thing I would change -- I wish I had a more powerful amplifier. I would go a step up from the amplifier I just quoted above. Mine is fine for most gigs, but I noticed it sounded quieter than I liked on near full volume at an outdoor gig recently. For indoor gigs, it seems more than OK.
Here is the one I wish I had've bought:
http://www.amazon.com/Crown-NXLS2500-0-US-Power-Amplifier/dp/B003HZV2OI/ref=sr_1_4?ie=UTF8&qid=1419560631&sr=8-4&keywords=Crown Amplifier
Remember, though, I'm a hack sound man. But no one is complaining. We run everything through the mixer (drums with kick and overhead mike, the bass, a microphone for sax or flute, guitar miked, and the keyboards) and it's working out just fine.
Good luck!