Welcome! I'm a graduate student too and know what it feels like to live on a "student budget."
With that said, our little guy Padre has not been without...not even for a second! It's hard to sum up how much they cost since it all depends on each individual dog. I can tell you my experience and hopefully that will help. Aside from the initial cost of getting him, we spent the first month or two in and out of the vets office which my husband then started to call Padre "our little Mercedes." His blood sugar kept dropping and they thought he might have a liver shunt so we did lots of tests, etc... After the first two months, he's been healthy, healthy and not very expensive at all. Our expenses for him end up being about $150 a month.....that includes food, treats, toys, dog walker, etc.....and we live in one of the most expensive cities in the US. you're smart to do your research beforehand and you will absolutely fall in love once you make the leap!!