I went the pc fan route on my 3 incubators. It cost me just under $10 for each 3 speed pc fan at Office Depot and Staples.
It took asking a couple people in the chat room to figure out how to wire a 12v dc pc fan in a 110v ac incubator.
I found by frying a fan that ac and dc do not work well together!!
After talking with people in chat, I found out to use a couple old cordless phone plug/cords. I used two 12v and one 9v adapter/cord/plug.
The pc fan has 3 wires, white, red, black, the cordless phone ac adapter has a negative and positive wire.
I stripped the wires about 1/2 inch, connected the red to the positive, black to the negative, using wire nuts, and left white alone.
I plug them all in and they worked.
So, with one hour of work, some on hand junk, and $30 worth of pc fans. I was able to turn 3 still air incubators into incubators with fans, for the price of one factory built fan.