A used 200 watt 10" or 12" powered speaker ($300). A speaker stand ($60). And a used 4 channel mixer ($150-175).
Alternately some speakers have multiple inputs and you can plug right into them.
Things I assume you have or will get: a mic, a mic stand, 2 mic cables (one for the mic, one for mixer to speaker), an instrument cable, an extension cord with 2-3 outlets (mixer and speaker).
Upgrades: a second speaker to use as a monitor, a third speaker and stand for rooms that are wide and need additional coverage, a graphic equalizer and some simple training on how to ring out a speaker.