if you're looking for only pre/power you could go with a QSC RMX850 (puts out 600 watts at 8 ohms bridged-good to have a little headroom). The QSC could be found new for around $300 or used on ebay for $200.
The preamp choices are many. Ffor new you could look at the BBE Bmax or Sansamp RBI both less than $300 new. Or for a used preamp you could get the Peavey Max, Yamaha PB-1, several Ampeg preamps. All these could be had in the $150-$250 range.
Throw it all in a 4-space (extra space for the future) rack off ebay for $50-$100 & you could have a very giggable rig for anywhere between $400 to $700. Not bad.
Numerous cab manufacturers out there also putting out decent quality cabs also. Avatar, Dr. Bass, Ashdown (MAG series), Eden (Nemesis series). all those in the $300 new ballpark.
Any combo of rigs I would be satisfied with gigging and all for around $750.00-1000.00 total for cab, rack, preamp, power amp.