The SiS 735 chipset is fast with SDRAM and DDR and on the K7S5A motherboard, you get 2 of each slot. It's not as fast as the current crop, but it wasn't far behind the Via KT333 and although limited in overclocking options has been improved with hacked overclocking BIOSes and there are many modifications out there for it, along with socket wire tricks etc, that mean you can do what you want with it, if you're prepared to take a little trouble.
So, if you pick up a K7S5A or K7S5A pro cheap you can run SDRAM on it until you can afford some DDR, and you'll have better performance than one of the rare KT266 or A boards that had 2 of each slot on, and better user support for mods.
I got mine used for like $25 and new they can probably be got for $40 or less, the deals are out there if you look.
regards,
Road Warrior