MacBooks last a long time, and even used ones are not cheap.
My current MacBook Pro (typing this response on it) is “Mid-2010”. Works great! Running Yosemite (actually - I’m in the pre-release program - so running “bleeding-edge” OS).
One of our other household computers still used regularly is a Dual G5 PowerMac... I bought it used not long before the PowerPC was dumped for Intel Inside... Other than a rapidly disappearing pool of current software, it still runs great - and is surprisingly nimble.