I'm sure you know that building your own desktop would let you get a vastly superior machine (in terms of raw performance) than buying an Apple. What you may not know, being out of the game for so long, is how much EASIER it is now. I don't build machines that often (maybe 4 in the last 5 years?), but when I do, I do some research, buy the parts, and then put them together. Then it works! In the 90's and early 2000 years, this process was a real hassle.
Sometimes you run into weird issues (especially with weird on-board video configurations), but I've never had them bad enough to make the process longer than a weekend day. (In the 90's it could take a week or more).
Is it easier than buying a Mac off the internet? No. You may easily make up your cost in time with your newfound productivity, though.
(Or you can just install Linux on your Mac directly, instead of a VM).