At Home Strength Training Suggestions for Lower Body

I want to add strength training to my routine along with the cardio I'm already doing.... but I'm hoping to do it at home and not get out in the nasty Atlanta rush hour traffic. I have some 10 pound weights to get me started on my upper body but am wondering what will work for my lower body.

The problem is I have bad knees and can't do squats and lunges without pain. I'm thinking some sort of resistance band type setup, but before I go out shopping, I thought I would get some recommendations on home equipment that would be:
1. not too expensive 2. easy on the knees 3. easy to store when not in use.