I picked up a Diamond Viper V770 which is a 32MB AGP card running the nVidia Riva TNT2 chip. It's in an older ASUS P2B motherboard, but it rocks pretty hard for this Windows 98 build (which I'm actually typing on right now using Firefox 2.0!). I got it off of Ebay for $10 USD. CRAZY! The Voodoo2 SLI cost me $76, and that's just the cards. I had to cough up another $10 for the SLI cable and around $15 for the VGA pass-through cable. So $100 out the door just for the Voodoo2 setup. And since I tried to swap out with an existing Diamond Monster 3D II 8MB card, I can't get the STB cards to work stable and consistently. I just put the Monster back in and it works flawlessly. Then agian, I AM only running a Pentium II 350MHz in mine. It was originally ordered for me back in 1999 while I was in college. I got the minimum processor that would get me 100MHz bus and RAM speeds because I knew it would help performace in games without me spending a small fortune at the time.
So if you want a build, let's list the stuff you want. Motherboard, Processor, RAM, Hard Drives, Optical Drive (CD-ROM), Case, Power Supply, Graphics Card, Sound Card.
For me, when I spec'd my system in 1999 in college, I knew motherboards still had ISA slots and that's where your money is for old legacy DOS games. It would have been a fight to get a PCI sound card to work right in those games and my MB only came with 4x PCI slots anyway. That gave me 2x ISA slots open to use. Might as well, right? I had no idea at the time that the Creative Labs AWE64 Gold ISA card I bought at the time would be such a beloved sound card among audio enthusiasts for doing music work including MIDI. It had 8MB of onboard memory for soundfonts. I honestly never used it, but that card was a BEAST with any DOS or Windows game. I never had problems. In my current re-build, I had to get the closest thing to avoid spending $150+ to get another one....I got an AWE64 4MB version....like a step down. But it's ok. Works like a champ too.
You probably don't need to bother with a floppy drive unless you really have a need for reading disks. Once I flashed my BIOS to the latest version, I removed the floppy drive from my system entirely. Everything I need is either stored on my 40GB D: drive or can be copied to the system via my home network from my Windows 10 PC (doesn't work the other way, unfortunately). I even copied the contents of my Windows 98 CD to my D: drive. It's really just copying the Win98 folder off the CD. Since I only had the C: installed in the system when I installed Windows 98 on it, it assigned D: as the CD-ROM. Now that the 2nd HDD is in, IT has D: and the CD-ROM drive gets E:. This way, any time I have to do a driver install - you know how they always ask for the Windows 98 CD....now it doesn't. It automatically looks for D:\Win98, finds it, and loads whatever the hell it wants without bothering me or wasting my time. It's very handy, actually.
Just giving you ideas for your build. Especially wanted you to know what I paid for my video cards for my Win98 rebuild.
Eh, someone just posted before I could post mine. Hmmm. If it was me, I'd go with the Coppermine P3 with a 133 MHz bus. That's really going to smooth out data swaps from the CPU and the RAM. Plus the Coppermines had 100% speed CPU Cache, not like the slower Katmai P3 versions. Find PC-133 RAM...256MB would be a LOT of RAM for a Win98 build and the games at that time really only asked for 16MB or 32MB of RAM at the time. I'm running 256MB PC-100 in my rebuild here and it's smooth as silk, doesn't run out of space, even THIS WEB PAGE works properly in Firefox 2.0! WOOT!
Happy hunting!