I'm currently in grad school in a 1BR apartment and I have a cat.
Even with her fancy grain-free food her costs (food, litter, registration, vet nest egg) is only about $80 a month, tops. Your funding structure may be different from mine, but our family of 2+kitty is able to live, if not luxuriously, quite comfortably on $20k/year if we had to. My sister is also in grad school, and struggles a bit financially caring for her cat, but he's a geriatric case that has quite a few medical expenses attached. (And, tbh, she has a higher cost of living than I do, with car payments and old loans and etc). Many of old-cat's current problems were/are preventable with appropriate care during their younger years, but hindsight is always 20/20, right?
In terms of expenses, honestly, the biggest unexpected one that I've run into is arranging for her care when I have to go to conferences. $25-$40/day for someone to come feed her really adds up - but compared to the actual costs of attending/presenting/printing it's not too bad. I just mention it because it's something a bit unique to the grad experience.
However, I'm not sure I can comment on the time commitment. My partner works from home so there's almost always a human companion around to keep Io company, though even when we're both home (on weekends) she spends most of her time amusing herself. A younger cat would need more of a time commitment from you. I also don't go out more than 2-3/week, and am an old person so I like to be home by midnight (don't want to turn into a pumpkin and all that).
Would you consider not getting a pure breed? I'm sure there are many many many
adult/middle-aged cats in shelters near you that are laid back and would love to have you in their life.
Others here would say not to get a pet if you're not in a very stable and comfortable financial situation. While it's a valid point, personally, I think the benefits to pet ownership outweigh the $80/month, and you're giving another living creature love and companionship and getting it in return.