Got high on Youtube courage here and just pulled the trigger on a highseer.com Pioneer unit. 12k BTU, 21.5 SEER rating. Something like $1100. It's maybe a little undersized, but I'm only trying to take the edge off - I try to feel seasonal variation in my house, too.
I also got annoyed with the local HVAC dudes, and went ahead and got myself EPA Section 608 tested/certified to buy refrigerant. About half an hour all-in, pretty much on high school physics and educated guessing.
We'll see what I really know in a week or two here.
Also, I *might* be able to talk Xcel into giving me a $300 credit here. They seem pretty contractor-focused.