I never borrowed money or sold stock; our company has grown on earnings. I did have $20K in savings and collected unemployment for a while.
Test equipment is amazingly cheap nowadays. A 30 MHz scope used to cost more than a Chevrolet, and now a 100 MHz Rigol costs about 2% of a Chevrolet. I paid 10 cents for a resistor whan I was a kid, and now pay about 1/1000 of that in real dollars. Google has made print advertising and trade show booths unnecessary.
You can generate a lot of value by assembling cheap parts. The trick is to pick the right product, design it reasonably well, and find real customers who need it, and give them good support.
Don Lancaster wrote a cute little book about starting a business; he sent me a free copy, can't remember why. He says that the first tool you need to get is some diagonal cutters, to snip the power cord off your TV set.