How to use an air conditioner port to bring in fresh air from the outside?
I assume you can just stick any appropriately-sized fan in front of the hole. For heating purposes, an air exchanger is designed to recover heat/cool from interior air before exhausting it to the outside, but it's annoyingly expensive for what it is. You can get air conditioners that have heating as well, (a heat pump is just an AC run in reverse) but it requires a bit of extra mechanics, so you won't find this feature on the cheapest ACs. You can look for, say, "Air Conditioner With Heat Pump", or "Air Conditioner With Heat", and get a good selection at the few hundred dollar range. 

Efficiency of a heat pump is above resistive heat, but still not great, especially for a portable unit. You should absolutely insulate the hose if you plan to use this long-term.