Having a window installed for a window unit or simply having the unit exit through the wall would be your best bet. Do you have a corner room with 2 outside walls? It would help to have some plantings to shade your outside walls. Maybe a vine of some type that would grow up and shade the walls. I would think that you could have the a foam type insulation injected into the outside wall without a huge expense. Also more insulation in the attic would help and a whole attic fan. Installing any of the insulation or attic fan is going to help with the overall expense of heating/cooling your home. Your local energy company probably has a program to do a free home analysis and will offer the most cost effective solution for your home. Check with them and see. Ann in TN