You sound like the perfect candidate for a bike - stationary or not. I have seen some stationary bikes in 2nd hand shops at pretty reasonable prices. You might try Craig's list as well.
The other activity that would work very well for you is swimming. Even if you aren't much of a swimmer now, leg kicks holding onto the side of the pool, walking and running in a pool will keep weight off those tender ankles, but still give you a great workout. I don't know if you have (or can afford) a YMCA with a pool near you, but membership is often quite reasonable.
Let's see if anyone else has some ideas.
2.5 years, 45 pounds later... 128ish pounds