I installed two Camframo 3 speed fans a while ago.
These were NOT low-buck
They work great while I am aboard, but I do not leave the boat connected to shore power when I'm not there. (Don't want to encourage galvanic corrosion, also don't want to find a charred hull at the bottom of my slip because I forgot to shut something off.
I wanted to keep the air circulating when I was not there to help cut down on mold/mildew and other nasty sources of "eau-de boat", but I did not want to drain my batteries...
I bought a 5W solar panel for $35 on Amazon.
When I leave the boat, I leave the solar panel on a cockpit seat and connect it to the 12V outlet under the companionway. My bow points north when I am in the slip. I turn the "Off, 1, Both, 2" battery switch to OFF (I also unplug the shore power at the dock box), but leave the breakers for the fans, and the 12V outlet on. When the sun hits the panel, the fans kick on and circulate the air.