This is pretty unusual for anyone doing it seriously. I've "flipped" (not exactly -- mostly major additions and teardowns that we hold for 6-12 months) the past 5 years and haven't met anyone who exclusively uses their own cash. We use some of our own cash, but you have to look at the opportunity cost.

The interesting part has been the interest rates. We started out borrowing hard money at 14% and are down to 7-8% now depending on the lender. Lots of cash out there chasing returns.