That’s what, an iMac G4, about 13-15 years old now I think (circa 2002-2004 or so I believe).
I think you’d be hard-pressed to find a 13-15-year-old computer still receiving security updates at this point (though you could toss a variant of Linux on there and be secured today if you wanted to make the effort). Feel free to plug in a Windows XP computer from that same era if you wish, but the odds of a 2002-2004 XP box being compromised versus your iMac isn’t even a contest. 
I used to agree with you on pricing until I realized that my many-hundred-dollar iphones have been sold for something like 60-70% of their value each year I’ve had them, and my laptops have sold for unbelievable amounts as well. My current desktop is from 2012, and not only still receives updates but is still “current” as far as Apple is concerned. I’ve spent at most a few hundred dollars a year on my phones, and I’ve had a new one every year as a result.
My two cousins (long time apple users, long before I switched in 2006) are both students, and get their $0 phones from their carriers and pay a rate that works for their budgets. I think they’d laugh at the idea that they’re in a high-income bracket. They’re both using macs from 2010 or so. They’re still supported and were purchased by their parents when they began school.
I look at your success with your iMac as a great ROI - it’s nice to see a system still humming along for more than a decade, that could be refreshed with a new install and might last for years more. Congratulations on keeping hardware around from that era, you have my respect.
