I just checked around at the various auctions..and you're right. Prices are quite high on this software..and they didn't use to be. When ME first came out, I got a copy for nearly "free after rebate"...and got rid of it after it crashed my system.
I think you'll find the price of 98 dropping after XP comes out in the next few months or so...but that doesn't help you if you want it now.
Your best bet, if you know some computer people, is to ask them if they've upgraded their system and will sell you their original disk at a reasonable price.
That's about all I can suggest right now, I'm afraid
PS - two more ideas, not as good, but maybe...:
1. Get windows 95 and limp along for now. It will do most things except the USB ports. Upgrade later to win98 when the price on that falls or you find a source. Win95 is much cheaper online.
2. search the system auctions and find a system that includes win98, and then resell the system without it (bit of work and a longshot, but there are systems selling for the same price as win98 alone...)