Keeping door and windows open while it's very cold or very hot outside can lead to extremely high heating/air conditioning bills. Meanwhile, high quality energy recovery ventilators that can exchange air with the outside without ruining your insulation tend to be a lot more than $200.
My home has very poor ventilation so I periodically will open the windows and blast a box fan to "flush" the dirty air out. If done quickly, there's not much thermal loss.
