Some G3s are Old World (the Beige Power Mac G3 and G3 All-In-One and pre-Lombard PowerBooks,) but most are Open Firmware. As far as I know, all the New World G3s use ATI Rage-series graphics (except the Blue & White Power Macs, which support a variety of PCI video cards.)
It is true that some MorphOS hardware can be had for a fairly modest price, but 100EUR is still a far cry from what you can get G3 hardware for - I got the Lombard for $10, and again, I could go on eBay and purchase a 400/500MHz Pismo, buy a MorphOS license for it, and total about what a lot of PowerBook G4s go for. I just think it would help lower the barrier-to-entry even further.