I'm pretty certain this won't be a popular answer: Buy a chromebook (Im partial to the Acer C720), install chrbuntu on it. then you have a cheap, light laptop with a small SSD in it. It'll be relatively fast. and only cost $199.
http
/blog.laptopmag.com/chrubuntu-transforms-199-acer-c7-chromebook-into-a-cheap-linux-laptop
http

/liliputing.com/2013/12/acer-c270-chromebook-tested-ubuntu-bad-200.html
otherwise:
step 1: find and buy cheap laptop.
step 2: create restore media if laptop doesn't come with it.
step 3: download linux install media
step 4: replace hard drive with cheap $110 240GB SSD and reinstall Windows.
step 5: install linux in dual boot configuration.
good luck in your studies.