Look for local ads. Garage sales. Some day one will be available for a decent price.
I started my collection with 2001-2005 hardware. So 3Dfx was not in my scope. When i expanded my interests to earlier things, i bought cheap parts first and improved my parts step by step.
In 2020 or 2021 i found a Voodoo banshee, mis-labeled as an SiS 315 for 20€ in a local second hand website.
In 2022 I bought a lot of two Voodoo 1 for 40€
A few month later I was given a Voodoo2 12Mb for free.
Only after that, I paid good money to get a second matching Voodoo2. This is the only one I paid 100€+. And only because i wanted a matched pair (Orchid Righteous 3D II 12Mb)
So. As an advice. Just wait and look for the deals.
By the meantime, there is a lot of fun to have with cheap parts you probably already have.
«Story in a game is like a story in a porn movie. It's expected to be there, but it's not that important.» - John Carmack
My collection (not up to date)