We've historically used computer fans, which obviously don't plug into an outlet, but a simple DC adapter (like this one on Amazon or pick one up at basically any electronics store or like look around your house your old router or whatever likely used one) will fix that. You cited time concerns in not wanting to use an inverter, but honestly this shouldn't add more than, say, 5 minutes, especially if you're already making a trip to the store/waiting on shipping from the internet for the fan.

EDIT: Just to clairify, pretty much any adapter that says "Output: 12 V DC" on the back will work (assuming you have a 12V fan, which most seem to be)