As far as spec and price a 5kw unit could be supplied for sub £500 Which is more than enough to provide steaming hot water on a one man system.
I am yet to build a two man system but it will come no doubt once I have time.
Another thing I did just for fun was make a little Bain marrie on the heater!
Put a tin of soup or all day breakfast in it half an hour before lunch and you have a nice winter warmer :-)