Back when I was living on my own in a college dorm, I had a little more freedom with how I spent my money, which is something I rarely had growing up, so I took to Amazon.
Turns out, as a student you can get 50% off Amazon Prime, so I definitely got in on that. I don't know how I still have it though.. Pretty sure it should've ran out 5 or 6 months ago tho, but I'm not complaining.
I don't order anything anymore as I've no need for it, but I take advantage of the free movies/shows on it every now and then.
As for sometimes going with a cheaper price or used items, I just look at the "Other sellers for this item" and find the cheapest price from a respectable seller.