I bought one of these: Whynter 11,000 BTU Dual Hose Portable Air Conditioner (ARC-110WD) ($350 on Amazon)

It's one of the few portable units that has make-up air provision for the exhaust heat. --that is, it doesn't suck hot air into the space being cooled; like so many other portable units.

Thanks guys! A little more info on my setup, the walls and ceilings are fully insulated and finished, the doors are insulated fiberglass, the side entry door is new solid core and seals well, and the one window is a nice insulated Andersen casement that I'm not going to hack up with a window unit.:) I'm really not looking to keep it 75 degrees at all times, but I'd like to be able to shut the doors, keep them closed, and crank the A/C to take some of the edge off of a hot day. Adding a little warmth in the winter would be nice as well. Sounds like the portable unit might be a good option, because I really don't want the hassle of a split unit.

Island, I was looking at a very similar unit with the separate intake/exhaust pipes on Amazon but at 14,000 btu. Sounds like you get more efficiency with the dual pipe setup on average.

Why not make a new opening for the window unit? That's what I did.

Definitely. I'm amazed that there are units that draw air from the room for the waste heat. But I suppose most people don't consider the (hot) make-up air that gets pulled into the room from the outside. I guess you have to be an engineer, or something. ;)

We're going to go with a roof mounted Hitachi unit to cool our equipment/ data storage room. It has an external condenser, and the evaporator looking unit sits inside. It can be set on very low, but the best part is that it's independent of the HVAC system for the entire building. It just removes heat from the small space that I want it to.

Edit: It looks like it's an inverter or mini-split.