Although it would be good to have more economic guidance, the prices of Pokemon are very abstract, due to the economy operating on a free pricing system - there are no fixed prices for a Pokemon, but rather they're negotiated verbally between traders. A multitude of factors can influence one's opinion on its value, including its IVs/proficiency against common pvp Pokemon/level among various other factors; however, due to many of the abstract base factors that causes prices to fluctuate, it'd be impossible to create an automated application to correctly reflect on a Pokemon's price.
As suggested, you can make a list of Pokemon and their respective price ranges, based on the general player consensus of a Pokemon's price to an extent, though reiterating, prices fluctuate constantly and it may be a nightmare to update the prices of all Pokemon. I just don't see it as feasible for any tool/application to automatically do so, however, due to many intangible factors influencing a Pokemon's price.
Hopefully when the auction house system is implemented on the playerdex, there may be more economic guidance as it provides to players a general feel on what sellers price certain Pokemon as, in addition to what buyers generally deem as a value for a Pokemon (depending on their bid if a Pokemon is auctioned). However, due to stats being a critical variable to a Pokemon's price, practically any price estimation could be a rather broad price range.