Yeah I used to run a monthly industry night. Very easy to get space on a Thursday night. They'd give us our own room that would otherwise be unstaffed on a week night. Tech nerds are very easy patrons. Not rude or unruly.
Like you said, just talk to the manager and say "hey I've got 50 people that want a place to hang out and order beer. Can we do that at your place or should we go somewhere else?". Easy win for everyone.
Running a conference is harder. Hotel conference rooms are way over priced. The AV prices are morally offensive.
If your attendance is under 100 you can probably do a restaurant. It will cost food and beverage but you likely just need to hit a $ minimum. Fees should be minimal. If you need conference space for over 100 I don't think there are any "good" options. And definitely no good options if you get into several hundred.