We paid about $12K for our 9 panel PV system and got 2/3 tax rebates so our net cost was about $4k. We will likely get it back in a few years from savings in electric bills which were about $100/mo. We did have our roofer evaluate that our roof has another decade or more of life before we put the PV on. It. We were told by the PV company that they could remove and re-install the PV on a new roof for $500. We have no regrets.
The PV installation companies all analyzed our electric bills and gave us quotes before we chose a company that was highly recommended by friends.
I would never choose a contractor by their ads or because they knocked on my door. Due diligence is highly recommended.