There is also the option of part-time consulting to pay the bills while building the startup. As a Django consultant, this person could probably make $50k annual income by consulting a few days per week. The rest of his time could be dedicated to the startup business.
Even if you have low living costs, you should still consider opportunity costs of not working. A consultant making $100k per year who takes two years off to do a failed startup has effectively lost $200k in income.
One recommendation, stolen from patio11: sell weekly blocks of your time. This is more fair to both those hiring you, and to your startup, because ramp-up and context-switch time are an expensive part of software development.
This is what I've started doing. Right now I'm consulting for a TechStars company doing some Akka stuff while I work on my own venture.
I'm single and 22 so doing this for a few months brings in enough to float me for ~year, not including the savings I had from the BigCo job I recently left.
The real bonus, IMO, comes from the fact that your former consulting clients are your most likely bet for job prospects if/when your venture fails, assuming they like your work of course.
Even if you have low living costs, you should still consider opportunity costs of not working. A consultant making $100k per year who takes two years off to do a failed startup has effectively lost $200k in income.