Put in a mini split. If you have an existing air handler and ducting then you could conceivably cool one room and recirc it to get budget cooling. This is what I am leaning towards for one of my rentals.
Mini-split can be done for $1500 in materials for a single, top-name like Mitsubishi. Then, if you don't have the tools and/or experience, pay an HVAC tech $300 to make final connections, evacuate, and charge the system. In my case I have started doing my own HVAC so I'll just buy a vacuum pump and hoses next time.