As a suggestion, you'll want to measure the flow rates of the points of use that will be served by the tankless heater. You can get smaller units that are intended to just serve a single point of use - larger ones are available for serving a whole house.
I got a bit of an education on these a few years back when we built a new home (in OH). The sticking point ended up being the fact that we were going to have a large roman/soaker tub. The flow rate for the faucet would quickly exceed the ability of a small point of use heater to keep up. (Some faucets will flow a surprising volume of water!) So we would have wound up having a large tankless heater to handle the bulk of the house and a separate one to serve the tub.........which would be rarely used but we didn't want the hot water volume to be an issue when it was going to be used. Cost started becoming the concern so we reverted back to a standard water heater tank in the basement - better safe than sorry!
Our water heater tank is also served by the geothermal heating system we installed (with a gas-fired supplemental furnace) so that helps a good bit with keeping the water in the tank up to temp. And our largest monthly gas bill since we moved in two years ago has been $52 in the dead of winter in OH. I don't know that any concept of cost savings, at least in our case, would have been worth the additional up-front cost of the tankless heaters. Our case is perhaps unique............yours might differ.
Conclusion: Check the flow rates for the fixtures that you want the heater(s) to serve - and also check into what the potential energy cost savings could actually amount to.
Bill