I built one of these earlier this year.

http://www.doityourself.com/stry/oldwindowuses

and built it to fit the windows I had available. I guess it took an hour or two and was built entirely from scrap materials. During the early Spring I used it outside to start off seedlings. Then bought it into the GH to give the Peppers a head start. The only thing I'd recommend is using a thermal blanket over the glass at night time when the temperature drops down (and then remove it during the day).

Thanks...I'll take a look at your link suggestion. My husband is very handy so anything that can be done...he can do it. We have several of those thermal blankets from the dollar area of Target. This could be a very affordable project!

Lori