I should have said aerator. Here's one for example. It's 1 watt.
Your PC fan idea might work for a more even aeration but it would take more to install.
Maybe Inkbird makes small thermostats but the one we have in the brooder is pretty big. I'd say it's 4" tall by 1.5 " thick by 2" wide, so pretty big for an incubator unless you were keeping it outside and running the wire into the incubator.
For a fan, the only idea I can think of is to get...