There are still absurd amount of computers available on eBay. They are not newest, but you can use them for most of the work and it will force software developers to optimize their programs, because ability to run software on 10-15 year old computer will become a competitive advantage.
Not only that but if you're not trapped in the Microsoft hell of forced hardware updates there's no reason to move on from what you've got now. My desktop PC is from 2007 and, for what I use it for, not noticeably different in operation from what you'd buy now. The only change I made was upgrading to an SSD at some point, apart from that it's the original hardware.