I'd use appropriate affiliate banners in rotation, based on users topics/interests. It lets you control what's going to be shown and payoffs are generally much higher than ad networks.

I tried that in 2014-2015, but it didn't make enough money. The chat room costs about $10 /month, but the affiliate program only brought in $3-4. I'm hoping to find something that would pay for impressions rather than commission on the sale.

Or any other unique ideas... the system I'm using does allow me to link keywords so I could sell ads based on that, but I don't know of an automated system for it that doesn't require local sales.

Any experiences with a pre-roll ad before they can start chatting? It looks like I have about 2,500 log-ins per week, so I would guess anywhere from 8,000 to 10,000 per month.

other than manually selling local ads

A chat room with lots of locals sounds like a great place for local businesses to advertise, and they'll likely pay much more than any ad network or affiliate program you can find. Why not go down that road? You could even make it self-service if you don't want the maintenance.

I do sell local ads (but I haven't had them in the chat room), and I built an Ad Manager a few years ago so that they can enter and create their own info on the fly. I have a flat monthly rate, though, instead of per-click or per-impression.

But for whatever reason, local ads have never really taken off, to the point that they're barely worth the real estate! They used to make about 4 times what they make now... I'm not sure if it's because local users complain about negative business experiences so I'm blamed (we all know that small businesses are held to impossible standards), or because I need salesmen (which is what I suspect), or something else, but I'm seriously considering replacing the local ads with lead-ins to other pages on the site in an attempt to increase pageviews.