Speakers - lots of good ones out there. Which would be best on your budget depends a lot on the actual dimensions of the room, wall surfaces, height of the ceiling,
etc. I'm assuming you're planning on upgrading just the speakers, not the whole
system, in which case what you need is something that will work well with what you've already got - how many amplifiers of what kind and
power, active crossovers and type, other electronics available such as delays to allow speakers placed further into the room to be phased with speakers near the
stage,
etc.
The last theatrical production I was involved in was Kismet, at
Crown H.S. - in 1968. There are others here, though, especially Wolf, Ship, Cruiser and Jo-Jo,
who could write an encyclopaedia of theatrical sound. lights and general theater tech stuff.
On a tight budget myself, I kind-of lean toward
Peavey for my speakers... but I do sound for low-budget rock concerts. There are other speakers that sound better, or are more efficient, but my gear gets set up in a different
venue every night, sometimes with pretty flakey
power, often with volunteer "help" that's none-too-gentle.
Peavey speakers and amps are generally pretty reasonably priced, sound pretty good when set up properly, take an awful lot of abuse and are fairly easy to repair on the rare occasion when they do break.
John