There are attempts that can be found online, quite probably even here in the archives, to use a formula to calculate individual stamp values based on relative face values of the stamps in question. The goal is to give greater weight to the stamps with higher face values, presuming that there would be fewer of them.
As I understand the concept, if a set has a total face value of 3 zblodniks, the 1-zblodnik stamp should represent one-third of the set's value.
Obviously, an imperfect system, and one which doesn't account for stamps printed in complete sets for sale to dealers (where all numbers should be approximately equal), or sets where the issuer seems to have issued very few of one or two values, in order to drive up prices. And it seems completely unreliable for stamps that actually saw significant postal use.
The only reliable work-around I've found is to concentrate on pre-1940 stamps.
