What about a voice conferencing service?

I have been helping some people recently find a voice conferencing service.

This is for a religious meeting, held 3 times a week and just needs to broadcast the audio and need to be able to have people call in to hear it (no responses from the callers). Maybe 2-3 people a week may need to call in.

I would think there would be a market for this as I haven't found a LOT of companies offering it. There are several but it's not as saturated as VOIP providers, some are pretty expensive. The cheapest I have found is $20/month. I would really be great to have a per min rate too or per connection rate since some weeks nobody will call in, some only one, etc.