Slimline window air conditioners

I'm pretty sure that this issue comes up every year, but before the temperatures soar I'd be very grateful if fellow brownstone-dwellers could help me out.

We live in a ground floor apartment in Park Slope with no air conditioning. All our windows are barred, and the gap between the windowpane and the bars is barely 3 inches. I have heard and read about special slim window air conditioner units and would love to know if any of you guys have them. If so, where is the best place to find such units? We've considered portable units, but they are so expensive and we are not sure how much longer we'll be living in the apartment.

Thanks in advance for your help.