I guess it was 1984 when I got my first computer, a $200 Commodore 64. 28K of Ram. I guess it was '86 or '87 when I had a clone XT built with a 8088-2 chip and a 40 meg HD. A year later I upgraded it to a 120 meg HD. Man I was hot!
After that I bought a number of kits from TigerDirect.com. I would typically get last year's hot model for about $300-$350. I wasn't doing any heavy crunching, just mainly word processing, so any improvement would be fine.
I'd swap in better sound cards, video cards, larger hard drives, and faster modems. If I wanted to upgrade the CPU, I'd often also get a new motherboard.
Once windows started identifying your original equipment and not allowing you to swap in too much new equipment, that became a limiting factor for me.
I used to run a Linux box with a static DSL line, but that was 20 - 25 years ago.
I haven't built a box in years.
I'm currently running on a HP notebook with an intel core i5 processor. I have no idea what that means. But it is fast enough for me.