Usually facilities like that have some kind of a PA system. Maybe they have something your group could use?

A group I belong to did that a number of years ago, but it was a much bigger group and a full sound system which included two mic packs. They can be temperamental. You don't need anything like that though. The problem with using the facility's PA system is dealing with it when the A/V guy doesn't show up, someone has walked off with the mic. etc. For under $300 (perhaps significantly under) you can get a whole portable PA system. Many are also battery powered, which means no liability for tripping over wires and independence from wall plugs on site. It's important to try them out, however, because you want the voice to sound clear. Also make sure the size of the space isn't going to give it problems (i.e., make sure it has sufficient power and volume), and that it can be heard as clearly by someone in the fifth row with three bodies between him and the speaker as by someone in front, and without blowing away the person in front. Speaking sound doesn't have to be nearly the quality as singing sound, however, which means you should be able to go pretty cheap. The main thing is you'd need utter reliability from whoever has custody of the unit and duties to charge the batteries.

A couple months ago, I did research on this subject, trying to find a way to amplify my voice to speak to someone who is hard of hearing. It seems like it would be easy and relatively inexpensive. I tried one item, around $50, and it failed.

I would suggest asking the group if they know anyone who is into audio as a hobby. Likely they could design a microphone, amplifier and speaker system for you. And many audiophiles have extra parts lying around and they might be able to donate some of the equipment.

Thank you for these ideas. I will investigate the issue with our group, but in the meantime if anyone has other ideas, I would love to hear them.

If anyone has a portable karaoke system that will work just don't add the music, use the microphone and amplifier features.

In a small group one of these might work OK.

Headset and amplifier

Ravencajun, that is similar to the one I bought and returned:
Headset and amplifier

The reviews were quite good on the one I linked but I have no experience with it. Another option for a bit more money would be something like this. Again reviews seem good but that's all I have to go by. That one of course has to be plugged into an electrical outlet.

Wireless system

The product linked in the preceding post is a wireless microphone setup - two microphones send their signal cordlessly (using radio waves) to the base station. To hear the signal, the base station needs to be connected to an amplifier and it in turn to a speaker (or an integrated amp/speaker system).

It's not a PA system, it's an inexpensive cordless microphone.

I don't follow. Do you have a PA system or not? You mention a lapel microphone might solve your problem and to me that suggests you have a PA system. In a large area like you're describing you do not want an omnidirectional microphone since that will compound feedback from the echoing.

I haven't looked at new portable PA systems for a long time so I have no idea what prices are. However if someone has a stereo system with a microphone input you could use that as a makeshift unit for the cost of a microphone. My old CB radio had a pretty darn good PA ability on it. A small bullhorn made a good clear PA for certain needs. You don't get much more portable than that. Granted it's not common equipment anymore but look around and think outside the box. Check pawn shops too.

Cheap microphones give cheap sound. If you have to buy something you can probably get a professional quality microphone for $100 or a little over. For example, last time I checked, an EV 635a was running about $100 and that's the industry standard warhorse microphone for ENG for close to 50 years now. Cheap mics can be $50-$75 easily.

I would check with the building you use and see about a PA system. You certainly don't need any sort of technician to run it for you! It's a matter of plugging in a microphone, flipping on a switch or two and probably adjusting the volume. Not complicated at all. And they probably will have it set up before you get there and take it down for you afterward.

If you want to buy a system, I'd advise against battery systems unless the battery portability is required. I needn't tell you when the batteries will die. If you really want to buy a system, check with a couple of your local school systems and churches. (Check with them anyway, sometimes groups are able to borrow things at no charge.) The purchasing department or AV department at the schools or the media/AV director could probably advise you on where to buy, what they use, the durability of the units they've used and even connect you with their vendor(s) who probably will give you the school's discount. If the group is one they like, you might get the vendor to donate a unit too. Don't overlook that possibility. Also, if you time it right you might be able to pick up a used unit from a school since now is the time of year they generally are spending their capital outlay dollars for the upcoming school year's equipment acquisition and replacement purchases.

Thank you to everyone for these ideas. Now I have some information to take to my group for discussion. It's possible, as suggested by Snidely and Cynic, that our building has a system that we can use; if not, we will investigate other ideas suggested here.

The thing about the a/v tech showing up isn't to run the system -- it's to unlock the storeroom! Major voice of experience here. Depending on someone else's equipment, someone who doesn't have a stake in your group, is a lot chancier than having a battery die.