Most provide useful tips for you in prior replies. It's true that most phd have a decent life here because the scholarship package is designed to guarantee you can pay your daily expenditure, plus the scholarship will be adjusted upward according to CPI inflation. Plus if you have enough energy, you can be RA for professor, then you will get extra $$.
But what I want to emphasize here is that, it is lucky enough you have phd degree without paying tuition and living expenditure from your own pocket, thus saving money is not your first priority. Because you will find that especially, from the latter half journey of your phd study, the brain work is very very intensive and you may travel around to build up your research network, thus eating well, sleep well and keep a happy mood are the most important. Invest your money in the right way. If you're excellent enough to find a faculty position here, you will find that the money you save these years is piece of cake compared to your salary.