It sounds like all you need to to get some airflow through the room, so rather than going to all the expense of AC it may be easier to put one of those air grates in the bottom of the door, and an extraction fan in the ceiling to draw the air through.

You may though want full AC if you are planning to expand your server room though.

Also, if you do go with the fan, don't put the switch next to the door, otherwise your janitor will probably turn it off when he leaves