Need advice for small orchidarium - little space, little cash

[plantaholic]

I have two masdies and a scaphosepalum micro... that are currently surviving in front of a humidifier in a larger indoor greenhouse. Summer is coming and I'm no longer going to be able to depend on opening the back door of the house to cool things down. I want to be able to have a small container for these three orchids but don't have a lot of cash or space. Any ideas? I know I need air circulation but I suppose just venting the top wouldn't do it for these babies of mine. I can keep it in my front north bay window which should be enough light. African violets do beautifully there as well as my miltonidium. I have a ten gallon aquarium tank that might do....