Steve,
Can't be any such animal in bonsai. Bonsai is art; valuation of bonsai is subject to a host of subjective criteria, which cannot be accounted for on a "form." Many aspects of
quality can certainly be accounted for, but that is only one small part of the "proper" value of a bonsai.
If you were to come across a form or formula to place monetary value on paintings and sculpture and musical compositions, and paintings and sculpture and musical compositions were transitory and ephemeral, you could use the same form for bonsai. But then, you'd wake up.
;-)
Kind regards,
Andy Rutledge
www.andyrutledge.com/palaver/main.htm
zone 8, Texas