All students at my school were required to have access to a Windows laptop, so keep that in mind. I definitely recommend getting a mediocre laptop and dual booting Ubuntu and Windows, especially if you're a CS student. Don't fall into the trap of thinking you need a shit ton of processing power and RAM to get through college. I have shit running on a Pi that's a million times more CPU intensive than anything you'll do in school. It's absolutely worth it to sacrifice power for portability. Just don't download a ton of adware and you won't have any problems. If you absolutely need a powerful computer (e.g. games), I would recommend getting something like a Lenovo Ideapad (about $160 and 2lbs, but still powerful enough for taking notes and running whatever shitty Windows software your school partnered with) and putting some money into a decent desktop. If your budget is $800, then that gives you $640 to spend on a desktop, which is more than enough to get you a good starter PC, and you can upgrade it as you go.