Tankless Electric Water Heater
Typically come in the 3kW variety, but more advanced ones are 1.8kW. Otherwise, 1.5kW are mini-tank, not true tankless.
- 1.8kW electric on-demand water heater - $159 - comes with aerator, 0.21 gpm activated, limited to 0.32 gpm. . 39F temp rise at 0.32 gpm. 
- Cheapo point-of-use on-demand electric - 3kW - $68 
- 3kW on Ebay, $60 - 
- 2.6kW - 60F rise at 1GPM - on the shower itself - 
About 1.5 kW - worst of 2 worlds - don't have enough continuous hot water, and waste energy. You can tell by their larger size than true tankless.