Sharing my recent experience. We had a 75 gal gas fired hot water heater leak. Went to store with intention of replacing it with new tankless system. Cost of tankless including equipment and install from $3800 to $4300 (got 4 difference quotes). And federal rebate calculation which has a very convoluted calculation was only $700. TOTAL Cost for traditional (installation and equipment) = $1200 . Man it makes doing the right thing impossible these days.
I'm installing solar for HW, it won't work year round for me w/older panels
Right now I have (1) 4x12' panel heating my hot tub ~450g of water to 108
Output is around 124 degrees at times
I have some more panels that I will connect to heat water for the house
So far with 6 panels I have spent ~$300
My electric bill last month was $100 less then it used to be
From the posts on other forums your savings with a tankless are not as high as the salesmen tell you. If you have a regular gas water heater (not power vent) you will still have hot water if the power goes out, with a tankless you are SOL!