Stop being a sucker. Personally, I'd tell the owners 10% or two weeks, their choice. Be willing to be negotiated down to maybe 3%. If they can't do that, then they can find a new lead dev.
And get some health insurance. I just broke my ankle (well, not really -- I popped my foot out of the ankle socket, severed 2 ligaments, tore a 3rd ligament, broke two bones, have $1k of titanium holding stuff together while it heals). The bill is $50K and counting with tons of physical therapy and another surgery to come. I'd seriously question any employer that can't at least buy minimal coverage for employees. Sometimes shit happens out of the blue -- I at least did this snowboarding, but my brother did something similar slipping in a parking lot -- and you'll have a medical problem that requires spending a lot of money. Make sure this doesn't ruin you, either financially, or physically by not getting the care you need when you need it.
edit: start here http://yclist.com/ I bet a ton of those companies need a full stack web dev.