We gig quite regularly and we have a full blown PA (with subs) even at small shows in bars. Why? Because we get a more even sound throughout, regardless of volume. Using the whole PA doesn't mean we are loud (well...too loud for a given room anyway). We always get compliments on how good we sound and many thanks from the bartenders/owners for not being too loud for them (even though at a new place that's small they get concerned when we start hauling in the gear

). It isn't that big of a hassle since all our gear is in our band trailer and available every gig. The whole PA (and it is quite substantial) only takes us an hour tops to set up and do a sound check, and perhaps an hour or longer to tear down depending on how much fun we are still having at the end of the night.

As long as everyone helps haul the gear and has a specific job to do once it's all inside (I hook up all the lights), it goes amazingly fast.
When you rely on solely the stage sound and only use a PA for vocals and maybe another instrument, it can (and usually does) sound uneven depending on where you are in the bar. A full PA will make you sound the way you should everywhere in the bar.
We are a 5 piece band and all have wireless units, so we can all go out and check the sound throughout the gig (although one of us will play the drums so the drummer can go out and get a listen on his drum mix before we do the whole band check).
If I were you, I would have every member of the band learn to use the PA. Learn how it is set up and what every control does, with every component. The benefits are more than just everyone having the ability to control it, it also helps when someone can't get to a gig early enough and that someone is the only one who knows how to set it up and do a sound check.
We are in a similar position where paying a sound guy just isn't worth it right now. We do have a roadie who gets a small cut for helping haul and setup everything (he does not hook up or have anything to do with using the PA). He's a trusted friend who is at most all of our gigs anyway. Besides the small cut, he also gets the free drinks and/or food (depending on the gig) so his small take at the end of the night is fair compensation as he would probably be at the gig anyway in the audience. This way he gets to go out and drink for free.

I wouldn't trust him to run the PA as our soundman though.
Honestly, good soundmen are hard to find around here. There are tons of people who think they are qualified, but aren't. If it's mainly bar, corporate/wedding gigs then running your own sound is so much easier. If the band members don't really know all that much about it, you could always hire a soundman just for training purposes to show every member how to hook it up and how to run it and do soundchecks. Once you know how, it isn't that hard to do.