Most PC laptops are worthless after 12-18 months of use. You either give them away or throw them out. If you buy a low-end system it's junk, and if you buy a high-end one, the only people looking for such a system would want to buy it new anyway, so you're stuck in a trap.
A MacBook often sells for a minimum of 50% of its purchase price if in good condition, possibly more depending on demand. The metal cases generally hold up a lot better than the plastic housing on less expensive laptops.
I'm on a Lenovo x220... it's plenty fast for most of my work. runs ubuntu like a champ. has, hands down, the best laptop keyboard that's ever been made. and only cost me $350, plus there's a strong aftermarket parts option.
Since i don't spend my time watching media, i don't have to worry about fancy monitors or display ports (though i could have gotten a Thunderbolt port).
This is a 5 year old laptop. The battery lasts at least 6 hours.
I'd say it has less value than five year old used underwear, but there's actually a market for that.
The last time I bought a Mac with an education discount, the computer was about 7% cheaper, but the AppleCare was 30% off. Not a bad discount overall, but not enough in the hardware department to break even on a resale, even new in box.
I used this approach in my student days and it worked pretty well given the very limited budget.