Rockii tree peonies germinate no more difficult than any other. The timeline on seed to bloom on rockiis in my experience and from experiences I have heard of growers is faster than say, suffruticosa. Those suffruticosas can take 7 years as I have found out first hand. Of course though, seeing that first bloom is well worth it. Once you reach that second year in growing that seedling, I feel you are in the clear and all you need to do is wait patiently for flowering!
As for price to pay, I have given a way seedlings that size that were unbloomed. Now if it is blooming sized, having bloomed, that price would go up to at least $40 would imagine. It all depends on what you find worthwhile.
