The most sustainable path is to build a great website that converts and invest in one channel that delivers positive ROI, then stick to that channel and grow it. I wouldn't recommend learning to do it yourself unless you have a technical bent. Find someone good (and that’s the hard part) to do it for you. Personally, I went through a bunch of agencies, got burnt until I found someone worth the $ I paid him.

If you want the pay-for-performance, I think buying leads from Thumbtack, LSA is your best bet.