I think this is a question that people run into a lot when starting a home lab and I think the way most of us start is by buying a new computer for ourselves and then using the old one as a server of some sort.
Back in the mid to late 90s (yes I'm old) I had a Compaq Presario (it came with Windows 95 and I upgraded it to Windows 98 and 98SE) and we upgraded to a Dell. I took that old Compaq and installed Mandrake Linux and that's where I started granted it took many years to get where I had actual servers running (I started in 2014 with actual real servers) but from around 98-99 to 2014 I almost always had a computer that I used for running Linux or just some random tool that I wanted to play with.
TLDR; you can start with anything, it just takes some inspiration.
Back in the mid to late 90s (yes I'm old) I had a Compaq Presario (it came with Windows 95 and I upgraded it to Windows 98 and 98SE) and we upgraded to a Dell. I took that old Compaq and installed Mandrake Linux and that's where I started granted it took many years to get where I had actual servers running (I started in 2014 with actual real servers) but from around 98-99 to 2014 I almost always had a computer that I used for running Linux or just some random tool that I wanted to play with.
TLDR; you can start with anything, it just takes some inspiration.