How necessary is buying a domain when I'm just a graduated student?
If your department/school won't give you support... 

The domain should cost you between $0.50 to $0.99 USD for the first year. Hosting costs range a lot, but many offer deals for the first year that cost about $12 USD.

After you have your own server and domain, it is trivial to setup WordPress on your own server. 

Thus you get the best of both worlds, extremely affordable and easy! Besides, I recommend most people have their own personal website for their portfolio and such anyway.