No car? Do you walk home from work? Take a route that has a park or playground on the way. Instant pull-up bars.
Go to school all day and are tired after? Get up an hour early and go for a run or bike ride around the block.
It's all about making time. You don't sound like you have a job on top of school so there are your weekends. When I was in better shape, I didn't set goals as to how many of a certain routine I would do - I would just decide what I was going to work on each day and put so much time into it.
Since I started working a lot more, I stopped having 'the time' - which is just an excuse for being tired or un-motivated.
Waiting to run until you get new shoes is the same as waiting to work out until you get into martial arts. You don't need the best gear or any gear to exercise. Muscles came free with the life deal. Set the goal of who you want to be and how you want to be seen, and go make all the small changes until you become it.
