In a parallel vein to the data collection going on over here I think we should start collecting the prices we have actually paid or received for buying/selling cubimals from/to each other.
If you found/left one on the street or got/gave one as a gift, that counts too; just record it as a transfer for 0 currants.
Once we have a bunch of data, we can actually track what the market price of the different kinds are. :)