Problems running

redskyharbor

Hi guys,
Due to having bad feet (they twist and tilt inwards, making my knees do the same, as well as my hips) I can't run or jog on hard ground, and can only just run on a treadmill, however I cannot afford a treadmill or to go the gym.
Does anyone have any suggestions of other cardio I could do?
Note I can't afford the gym, swimming pool costs, or equipment - student living and what not.
Thanks in advance x