It's simple supply and demand. I'm a bamboo hobbiest. So I feel your aggrivation. I am trying to justify paying $60 for a 5 gallon Ph. Nigra 'Daikokuchiku'... This, and there is no real evidence that it's large size is even genetic. (On the other hand, no other Ph. Nigra has ever gotten that big, so I'll pay the extra $20 and call it a gamble.)

But I also recognise that there are a lot of people who want this... If I had five extra plants and 100 people who wanted them, I would probably also price them accordingly.

eBay is helping though... It used to be that a common gardener like me who had an extra plant from a division would have no good way of selling it. But now, I can put them on eBay (as can a lot of other people who are waking up to it). So, prices are falling for the common species. If you just want a 1 gallon Moso, you can get it for $12.

Final note: A $10 #1 Moso will be well established in maybe 7 years... A $25 #3 might be that big in 5 years. Or, a $45 #5 plant might be that big in 3 or 4 years. So, you have to ask yourself, "Is having this plant big 4 years earlier worth $35?" For me, the answer is usually "Yes!"