I was doing some contract work on the side while building the MVP, but switched to full-time right after launching it. I wouldn't necessarily recommend that though.. basically burnt through all my savings over 4 months. Right as I was starting too look for more contract work I ended up winning a $15k grant from YC [0] which bridged the gap until I got to profitability. Now at around $6k - $10k/m (not recurring, so it varies).

[0] https://blog.ycombinator.com/announcing-the-startup-school-2...