I know that the thread is probably dead, but do you still need help with finding a cheap door? Recently I was looking for a new door for my son's room, it was really old and even had some scraps on it. A good friend recommended me this company called Door Design Lab for the new interior door
I needed, and I was surprised by how cheap the doors are comparing to the quality provided. I know that you are not looking for an interior door, but maybe you can find the one you need on their website. Also did you find the windows you needed? I would like to replace the windows in my garden shed and can't find a good company that sells them.