Good call Red. Right now, the 1.25 Mhz eMac is the cheapest system that will run MorphOS. Currently, there are a few on Ebay and one starts at under $15 (of course shipping makes that quite a bit higher).
I'm looking forward to Powermac support too, but rumor has it that the development team may only support the MDD models.
Personally, I'm hoping they'll support the Quicksilver Powermac as well since there are more third party CPU upgrades for that model.