In 1993-94, I upgraded the RAM on my home 486, which started with 4MB. I doubled that to 8MB for $250, then to 16MB for another $250, and finally to 32MB (the max for the motherboard) for another $250. At the time, I was a poor undergraduate and had to give up other pleasures for these expenses. If I estimate correctly it's about $30K/gigabyte (only high end servers at the time had a gigabyte, and they would often cost $100K or more).

The lesson it taught me is that swapping is slow and that if it happens during your software development, you're much less productive. When I finally maxxed out the RAM on my machine, I could run linux + emacs + X11 + bash + g++ all at the same time, making me about 10X more productive. It's an investment and lesson that has helped me build my career over decades.