Well, I guess we should go in between here. How about 150 for an egg, 300 for a pup, and 200 to train?
So...
Skills: Scorpion venom dogs have a +4 racial bonus on Jump and Spot. *Scorpion venom dogs have a +4 racial bonus on Survival checks when tracking by scent.
7 ranks: Listen 3, Spot 4?
That seems too cheap for a poison-attacking creature you can sic on your enemies.
I'd prefer something like 400 gp for an egg, 800 for a pup, 200 for training, and 1000 gp for a fully trained dog.
That and giving it Alertness, Improved Initiative, Track (B) all sounds good.
I wouldn't mind increasing the poison damage to 1d6/1d6 Con like the Viper Venom Dog, since the original has "save vs. poison or die".
Raising the price is ok by me; estimation by CR is tricky.
Agreed to those feats, too. I'll agree to the poison increase, and we should double check that the save DCs are a little harder than for the viper, since the original text said you save at +2 vs the viper venom dog poison but not the scorpion venom dog poison.