G.W.
I think it depends on what you do with it and how much you pay for it.
If you just use it for email, internet, maybe some word processing, etc. then I'd say you don't need to spend a lot of money on a big computer.
If you do lots of other stuff, even if it's just for a hobby, then you might need a bigger computer for the capacity (editing photos, graphic design, managing videos, etc.)
I think it depends on the computer. I've heard Macs last a long time but MAN are they expensive. My laptop was $400 (Toshiba dual processor) and I'm expecting it to last about 2 years.