After years of 'umming and ahhing' about it I found an new 8000btu/hr end of line air conditioner on ebay for a snip at £99.99 + carriage ( first time I looked these things were ~ £500 ).
It's only a few weeks each year here that you really can justify one but it makes the difference between getting useful work done and not much at all.
What's somewhat surprised me is that it seems only just to mananage with a room
15' x 12' x 8'6".Graham