The cost isn’t that bad if you are up to DIY. You can get 3 ton/36k btu mini split units that will heat/cool 1500 sqft for around 3k.

You have to have power pulled to the outdoor compresor, but otherwise you drill a first sized hole in your external wall, mount the internal “head” unit over the hole and run the power/compressor/drainage hoses down to the outside unit. Bend the compressor hoses into a bundle, plug everything in, turn it on. Lots of great youtube guides.

Depending on what the electrical runs costs you, you may be able to get it all done for 5k.