I still think they are very common. Although some people try to sell them for big bucks, I personally don't think they are worth it right now. $30 seems about average for a used G3 based iMac. Tons of schools and places bought them, so you have countless out there.. no telling how many are still in use (our school district just phased ours out last year..replaced them with HPs.. .

I wouldn't doubt theres still tons out there, I don't see them being rare for at least another 5-10 years or more.