If you continue to have difficulty finding a green plumbing pro that can install a tankless unit, or a reasonable price for the Phoenix heater, reconsider the solar thermal option.
In addition to a full 30% federal tax credit on labor and materials (with no max), Pennsylvania offers incentives as well.
The DSIRE website has more info on PA's state incentiveshere.
For more information:
Read Paul Rosen's Q&A "Can you tell me how well solar hot-water heaters work?"
Also, read Cameron Habel's Q&A "I've heard solar water heaters are expensive and easily damaged by winter freezes. Is this true?"