I install and service propane on-demand water heaters. Rinnai is light years above the competition, the unit runs about 900-1300 depending on where you get it from and installation is not much more 500-1000. These are AK prices so might be less in your area. They also make units for natural gas if that is an option.
The water flow is incredible 7.5gpm-9.8gpms at minimum delta T(temperature change) our groundwater here is about 40degrees and I typically measure about 5gpm. More than enough for a standard household. And endless as well.
The condensing models are capable of 96.5% efficiency although the steady state is about 98+%. Even the non condensing models are in the mid 80% range. Combined with not using energy while not in use, they are very energy efficient.
If two wrongs don't make a right, try three.