I got my PPL while studying for a PhD. I had little cash when I started - about enough for four lessons. But that was enough to make the decision to learn. You can keep putting it off, but you will always find something else to spend the money on. Do it now while you have few other expenses and a fairly flexible timetable. Once you graduate and find a job you'll notice that the weather at weekends, when you want to have a lesson and aren't working, is generally non-flyable.
To fund mine, I worked about 10 hours a week as a temp. Then, every other weekend, and sometimes mid-week, I would have a lesson. The rest of the money went on general living expenses. Budget hard or you'll find that an evening out with your mates can cost half an hour in flight time...