Although it would make things a lot easier, prices would change too rapidly for it to even be helpful. It would have to rely entirely on self-reported sales (car sales are obviously easier because they're heavily regulated). I've seen morphs go from $15,000 one year to about $300 a couple years later. The database would have to constantly be updated... even a matter of months without editing would make the whole thing a joke.
To figure out if you're getting a good price, search for that morph on faunaclassifieds.com and kingsnake.com, and compare prices. You also have to take into consideration the sex, age, weight, and even what the snake is eating (i.e. a female, two year old, 1400 gram coral glow eating rats will be worth +10 times as much as a male, two month old, 100 gram coral glow who refuses to eat anything but mice.)