If you want to build a Windows 98 retro gaming PC, prices might be not very friendly these days.
In my country, period-correct parts for Win98 are expensive, as PC were not very common in most homes and offices at that time, and now scalpers are collecting and reselling them as "industrial" if it supports ISA, at a premium.
However, OEM boards are sometimes the hidden treasure.

# Hardware config

1- CPU: 			AMD Sempron 2500+ @ 1.40 GHz 						￥10
2- Mainboard: 	ECS K8M800-M3 (Lenovo OEM)							￥100
3- RAM: 			1x A-Data DDR400 256MB, 2.5-3-3-8-1T				￥10
4- Graphics: 	PNY Verto GeForce 6200 AGP with 256MB of DDR2		￥75
5- HDD: 			Western Digital WD800BB								￥47
6- ODD: 			Pioneer DVR-118CHV DVD burner						￥75
7- FDD: 			None for now
8- Audio: 		Legend (now Lenovo) Audio Ace AA724-A2 with polymod	￥50
9- Network: 		Onboard VIA VT6103
10- CPU cooler: 	Random down-draft cooler with AMD mountings			￥10
11- PSU: 			Segotep 350W max									￥25
12- Case: 		Acer Veriton D430 case								￥59
13
14- Total: ￥461 / $65.46 / €55.91

# Motherboard and CPU
ECS K8M800-M3 (https://theretroweb.com/motherboards/s/lenovo-l-v800e) were manufactured in a large quantity for Lenovo's entry-level home and business PCs and now they're readily available on IdleFish (our FB Marketplace or eBay) for around 100 yuan, or 120-140 with a Sempron or Athlon 64 CPU bundled. They don't have ISA slots, don't do overclocking and generally worse in compatibility with everything before Windows 2000, so the prices are still friendly.

Mine came with a Sempron 2500+, with Palermo core and only 1.4 GHz of speed, it's fast enough (and not too fast) for Win98 and runs very cool even with this crappy cooler. With AMD K8 you can use modern AMD coolers to reduce costs and noise.

This board has the VT8237R Plus southbridge, with a revised SATA controller that supports SATA2/3 devices, but still cause errors under Win9x. When I first tried to install Win98 on this board it always freezes during second phase of setup. From PhilsComputerLab's video it was the SATA controller's problem. Unlike Intel chipsets, VIA doesn't support "remapping" SATA ports to the default IDE controller in order to maintain Win9x compatibility, so I disabled it and stick to IDE this time.

The BIOS is also troublesome, it has COM2 enabled and LPT1 set to ECP mode by default and cannot be changed by user. The MC'97 controller is also force-enabled but there's no such device requires it onboard and no CNR slot. I modified the BIOS, disabled COM2 and set LPT1 to SPP, so some resources are freed for DOS and Win98, but I didn't find a way to disable the MC'97.

# Graphics Card
I bought a MX 440-8x and a 9550 and they are all non-working. Then I got a new old stock GeForce 6200 and it worked like a charm! It is a low-profile fanless card, but runs very cool - at 25 degrees C room temperature, 47 degC idle under Win98, ~60 degC just after finishing 3DMark2001SE.

As for the drivers, avoid 81.98, as it can't detect DVI-D monitor properly: After setting the resolution and a reboot, the monitor results in a black screen, but the OS is alive. If I plug in a VGA monitor, I can see desktop on it, but the DVI monitor is still black, but it can work if set as the second monitor. This bug was gone after downgrading to 77.72.

# Sound Card
I went with my Legend/Lenovo Audio Ace, it was a common piece of hardware present in Legend desktops. It worked perfectly under 98, including legacy emulation under DOS and 98.

For DOS sound support, I went with the latest 3.16 driver and PhilsComputerLab's MS-DOS Mode Super Easy. I tested Doom, Quake and Rusty (a 1993 Japanese Castlevania-like game with great BGMs composed for OPL3), all of them worked out of the box with the default A220 I5 D1 T4 settings, both FM and PCM.

# Benchmarks
3DMark 2001 SE: 7778 (98SE), 8443 (XP)
AIDA64 Memory: Read 3137 MB/s, Write 3143 MB/s, Copy 2995 MB/s, Latency 53.6 ns
CPU-Z Vintage: Int 2872.0, FP 10431.2