What providers do you use and what’s the cheapest we mustachians can pay to get connected per month?
Well, the cheapest you can pay is $0, and use the library for connectivity.
For most use cases, a 5-10Mbit connection is usable. You're not going to be running multiple 4k streams on it, but... the streaming 4k stuff I've seen at friends places hasn't really impressed me. Sure, it's "4k," but the quality isn't much of an improvement over a 1080p stream, or 720p. You can overcompress and hash up any resolution you want, if you want to fit it in some low bandwidth pipe. It'll still look like crap.
It's going to be hyper-location-dependent, which you offer
no advice on. So, I could tell you what I'm paying, but it would do you literally no good unless you're in my neck of the woods.
I think I've got the highest in this thread so far - $125/mo. That's for two separate rural wireless connections that feed the property. One is 15/3 (on paper, closer to 10/2 in practice), one is 5/1 (backup connection, actually makes rated bandwidth most of the time). The slower one is used for bulk transfers (I sync things to/from my fileserver regularly, currently updating a local Ubuntu mirror), the faster one is for interactive content. But most of our media isn't streaming - we host it locally on Plex, and pull content in from optical media. Not a heavy TV household, by design.
However, I work from the property, and when one of the connections is down for an extended period of time, this causes a problem for me. I can tolerate shorter outages without an issue, but one connection was down for a week when a node went down in abnormally cold weather, which very much causes issues. So, the pair (running on independent backhauls - I verified this before getting the second one) works nicely enough, and is perfectly serviceable. We just don't pull down massive amounts of media, and I keep a local storage server for things like repos/ISOs/etc, since it's way faster than pulling it from the internet each time I need something.
You can function in the modern world on 5Mbit or so without trouble. Most places won't sell you that low cost of a connection, though, because the infrastructure is the bulk of the cost.