Looking at job listings, most places seem to say that experience with C# is required. Do I just need to keep looking, or are these companies possibly more open minded regarding previous experience than they appear?
Apply at jobs even if you don't have experience in the specific language, most of the time your fundamentals should carry you. If there's a specific role you really want, then make a side project on GitHub in the language you want to have experience in, and that can help get past any HR person that's just looking for a keyword on your CV.
A few weeks ago I talked to a recruiter who confirmed that I'm being underpaid. Since then I've struggled to stay motivated, but I also really hate job hunting/interviewing etc. I'm technically self employed, working for a single client, so I'm considering telling him that I'm going to take Fridays off. If he doesn't like that idea I'll start job hunting for real.
I think I need to move.