My first server was a single-core Pentium - maybe even 486 - desktop I got from university surplus. That started a train of upgrading my server to the old desktop every 5-or-so years, which meant the server was typically 5-10 years old. The last system was pretty power-hungry, though, so the latest upgrade was an N100/16 GB/120 GB system SSD.
I have hopes that the N100 will last 10 years, but I’m at the point where it wouldn’t be awful to add a low-cost, low-power computer to my tech upgrade cycle. Old hardware is definitely a great way to start a self-hosting journey.
In US metros, they’re typically around 2% of the home value, with discount maybe 50% for owner’s primary residence. Depending on the locality, the home value may be reappraised every year only only after a sale. If you bought a $100k house, planning retirement on $1000 annual taxes, and the area gentrifies your house to $500k, the extra $4k/year in taxes can be a budget buster.