Can you walk? This is the easiest, least expensive way to exercise. If you live in a safe area, a lovely walk around your neighborhood each day will eventually allow you to build enough strength that you'll begin to walk a bit farther, a bit faster, with fresh air moving through your lungs, feeding your circulatory system. It doesn't cost more than a pair of sturdy walking shoes.
If you don't feel safe walking outside, go to a mall and window shop until you build up enough stamina to walk faster and farther ... good scenery, benches to sit when you need to ... and if the aroma of the bakeries and other food vendors entices you, breathe it in, and use my imaginary diet - just tell yourself that you've just finished eating one of those delectable treats ... and sip some water.
Or best of all, walk with someone and treasure the time it provides for conversation ...