I have been, for the most part, working solely in theatre since school. When I first graduated, I moved to Minneapolis and took a temp job. 3 months into it, I got a daytime admin theatre job to support the work I was doing as an SM at night (totally unpaid at the time). I didn't like that. I left the admin job and started pursuing paid work. I landed a summer contract as a non-union ASM at a large theatre. When returning to the city from this, I was still working for small-med companies, so I got into doing promotions for a while.
Promotions is where you (sell your soul to satan) go out on the street, or to the mall, or to a concert, and help to advertise a product. I handed out apples from Target at a park, barked about a new BMW at a country music concert, set up a big Best Buy tent, did a This Old House road-tour stop in Minneapolis, gave out samples of Jamison at gaybars, coughed as the "mystery cougher" for Ricola, etc. etc. They weren't always fun but I always made good money doing them.
Another option between jobs is always filing for unemployment. It's there and it's meant to be used. If you have a few weeks of, file for it and you'll be surprised at how much a few extra dollars can help you out.
After a year of doing promotions about 25% of the time and SMing 75% of the time, I got to a point where I didn't need them anymore. Since then, for the past 2 years, I've not had to do a single promotion, a single day job, but ONLY stage managing.
For me, it was a HUGE ladder I had to climb. I came from college in Iowa, so I didn't have many connections except the few that my professors had set up for me...plus, I found stage management late, so I was behind anyway. My only way in was starting with the small independant theatres, which is where you seem to be, JJC98. It's a tough place to be, honestly, but it is possible to climb that ladder...and to do it quickly if you want.
Once you are making ends meet with SMing (or descent money for that matter) the key is to save save save save save! I started an auto-withdrawl from my checking and consider it part of my bills every month. My financial advisor says that I should have a backup fund that is 2.5 x my checking account balance in savings, and that my checking account balance should be 4 months of living expenses (including the current month)....now I'm not there yet with that...but I'm working on it, and if I have to go a few months without work, I have the security of knowing that I won't go hungry.
That's what I did. I'm now a full-time freelance SM coming from having a dayjob, no resume, and little/no real world experience. This is all since 2003. So, it's very possible and very do-able to make a living at it and to get your way up there quickly. It's all about commitment and dedication. Good luck!