I built a three thousand dollar workstation in 2014.
Intel gave me a free 4960x, which retails around $1000. I spent the other $2000 out of pocket on a system to match: ~$250 for the mobo, ~$100 for the case, ~$100 for cooling, ~$300 for the GPU, ~$300 for the power supply, ~$200 for a super high quality SSD, ~$200 for three hard drives, ~$50 for a media player, ~$200 for 32 gigs (4x8) DDR3 at a decent clock rate, and a 4K TV as a monitor, and taxes for it all.
(That's the computer crunching graphics.)
Given Intel's advancements in single-threaded performance over the past three or so years being fairly low, and my work there, I do assume they'll continue at around ~5% single-threaded perf year on year. They'll continue quite a large amount of power savings year on year. And they'll continue a lot of multi-core perf and graphics perf every year, in servers and client respectively.
Given that 1) I don't really care about having more than six cores (twelve threads), 2) single-threaded perf won't be rising too quickly, 3) power isn't terribly relevant for a workstation like mine, and 4) on-die graphics being irrelevant for both workstations and the server market (my CPU is a gimped xeon) - I fully expect to keep this computer with only mild changes for eight, maybe even as much as ten years. It's been two, and there hasn't been much to make my computer and slower than it used to be. Linux tends to get faster every new release anyways.
Of course, I do really use the full performance of the machine.
Speaking of resource-intensive programs - there are no games out, not even AAA titles, that really expect $3k worth of compute hardware, let alone $5k. $5k a few years ago is an amazing machine today, hardly worse in gaming performance than a $5k machine today. I guess I can see how to spend $5k on a gaming machine, but I have no idea what kind of hare-brained ass-backwards computer-spec-masturbating cretin thinks you need to upgrade such a system on any sort of regular basis.
That said, see if you can buy his old computer for cheap. I mean, it's crap now, right? See if you can buy it for a thousand bucks.