If you look into RV
equipment rather than
marine equipment, and then you might be able to find something under 2
boat bucks, and easy to install too.
But you need to be very careful: RV equipment is generally mounted such that fumes drain OUT of the vehicle onto the ground. On a
boat, fumes end up in the
bilge, and can (and do) accumulate to explosive air-fuel ratios, so a spark will explode your boat. Maybe you will survive the explosion, its amazing to me when people do survive such explosions, but sometimes it does happen.
If you go with RV (cheap) stuff, you will probably need to install it outside the boat, like on the swim step fully aft of the transom. Probably not the aesthetic you are looking for.
I use
propane space heaters in the
cockpit. I always ensure I've got multiple carbon monoxide sensors, and I ensure their
batteries are OK. Carbon monoxide is a silent killer.
Below, I use warm clothes and down comforters. Hatches are ALWAYS open for air flow. CO sensors tested and placed near pillows, on the floor, and near the ceiling. I never use the space heater below, I'm just being careful in case the CO gets into the
cabin from the engines or outside space heaters. Body heat does warm up cuddy cabins better than you might think.
The right way to go is to install either a
propane or
diesel marine system. These are not
cheap, and usually not easy to install. They sure do work!
For water heaters, there are many fairly inexpensive SS
tanks that are warmed by
cooling water">engine
cooling water. These are usually the best way to go. They warm up quickly and stay warm for a few hours after you turn the engines off.