While you're searching around online or in the wild ask your family and friends (older neighbors, etc.) if they have some stuff gathering dust that they would like to dispose of or sell. If people are aware of what you're looking for they can always remember of something they have, or even people they know that might have stuff too. You truly never know what's out there in people's attics, it's still perfectly possible to find lots of stuff. Either it will satisfy you or provide you more info and clarity to buy other things in the future.
If you want to dip your feet for the time being just to experience the OS and games I suggest the Pentium 4 era PCs, currently the "disregarded" generation, so they're much cheaper and commonly found than PCs from previous eras. I think Philscomputerlab has some YouTube videos about Pentium 4 Win98 builds on the cheap that work quite well. Phil always tries to provide cheap alternatives in the hobby which I very much appreciate, as most people don't get the YouTuber type level viewer donations, not even close. You will be able to experience lots of DOS stuff, and after some time with Win98 based games and DOS games you will know exactly what you want or need and more importantly what you're looking for, and that will give you the tools to really search efficiently.
For example, I started some years ago buying a P-III Celeron in a flea market by chance, and little by little upgraded the build to a 1Ghz P-III. Then my grandfather gave me his Pentium Pro that I used to play with in my childhood years, and I also found my Pentium IV build from the era in a family attic. After that I found myself lusting for a 1.4Ghz Pentium III-S Tualatin based PC, as Pentium III is my favorite era, so I started little by little gathering parts over 3 months until I finally build it. I didn't *need* it, but eventually realized there was a gap between my Win98SE and WinXP builds that I wanted to fill, but because I was prepared and informed I was able to gather the rarer than normal stuff to build it in that time period at good prices, even if it took longer than normal and was slightly more expensive than other things. But as said in posts above that's when the collector's tax comes into play. And lastly I got a full tower 486, a large tall tower case model that I could only dream of even seeing for sale as people recycled them by the hundreds in the 90's, and it practically never shows up for sale, whatever the price.
I only found this 486 that time, being the only occasion I even saw it for sale, because I knew that model quite well from research to the point where I identified it in a very blurry picture whilst browsing the ads list, with a very understated title. So if you have a clear idea of what you're looking for you will be prepared too. There are multiple ways to get what you want, and I still think it's perfectly possible to find good deals in this hobby for the time being, generally speaking. You already made a great decision registering in Vogons, people here really know their stuff and are super helpful, I should say! My 2 cents, best of luck