I use a portable Infrared Quartz heater. You can set the temperature of the room and it's extremely quiet, no noisy fan turning on and off. There are 3 settings (we use the medium room setting) to allow you to be efficient with your power consumption. You asked for cheap and it will blend in nicely with teak interiors
We have ours right under our captains seat.
Duraflame Williams 1500-Watt Infrared Quartz Electric Portable Heater - Oak-10HM4126-O107 at The Home Depot