Working backstage in a theatre is an interesting area with lots of career options. To start, there are various roles including directing/production, set construction, engineering, lighting, and costume design. Start by exploring which of those areas most interest you, since they each involve different sets of skills. After focusing on one area in college, you will find there are a number of different places to ply those new skills, both in terms of geography and employers.
With respect to geography, not everyone works on Broadway and has to pay to live in New York. You can find the same jobs at theatres in every city in the country (and around the world), often in areas that are less expensive to live. It is also easier to break into the theatre in smaller venues, then work your way up. As you do, your pay may rise, allowing you to afford to live in more expensive areas.
With respect to employers, you might just find yourself drawn to areas outside of the theatre and you will have core skills that are relevant to a variety of jobs. For example, if you work on electrical engineering for a theatre, you are bound to have skills relevant to electrical engineering in other capacities. Or if you learn set design, your artistic skills might be handy in a variety of places that need people experienced in carpentry and painting.
The key is to identify your general interests and strive towards a career in the area of your choosing. If you pursue something you love and you are developing core skills, you are bound to be able to find a way to make a living while enjoying your job.