Go to the largest gym (the one with the most equipment) and try all the equipment with the proper foot brace. You can usually get a free day or a week. Some even give you a free hour with a personal trainer. Rowers and recline bikes might work if not at least you can use upper body weights and abs.
If you find a machine that works for you buy the best you can. You can usually get Gym quality equipment on CraigsList.com for half or less then the cost of new equipment. People buy it and never use it and then resell it for dirt cheap.
There is also swimming. Contact your local high schools and Jr. Colleges and see when they have lap swim. Most people doing laps are so busy they are not paying any attention to anyone else so don't worry about how you look in a swim suit. Lands End has a couple of short style swim suits in larger sizes which I fee pretty comfortable in.
Curves and all those ladies quickie gyms will also work on a program for you. They are usually free for the first week also. In a circuit you will probably be able to do at least 2/3s of the circuit and you can then just repeat. This will keep you heart rate up enough to get good benefits.
Wheel chair sports are also great fun and you can do that. Most larger areas have at least one or two groups. For us with legs that we can stand on they will sometime loan a chair and allow you to play too. There is bicycle club in
Berkeley CA
that has hand pedal bikes they will loan out and let you go on group rides.
Horseback riding can also be a good way to get out and use those leg muscles without putting weight on your foot. Just ride western and have the stirrup on your bad leg lower so you don't bear weight on it.
If your heart is really into getting out and moving your body there are many choices but you’ll have to make a compromise or two and look around a bit.