"going rate" various from location to location and artist to artist.
i set my prices not the stores. i never do anything verbally - i have legal contracts and everyone is required to sign before i'll even cut fabric. it not only addresses the scope of the project but also the taking of pics, internet postings, and copyright issues.
my typical price is $50-$100 a square foot but if its highly embellished it can go much higher than that.