Laurie
Yes, both mine and the ones in the exhibition.
I've always held the mantra that you have to value yourself for your artwork to be valued. ThereforePut a price on the work that you are happy with, and refuse to be devalued through lower offers.
So, make sure you work out the cost of all materials used, postage, etc first.
Then as it's practically impossible to charge an hourly labour rate, decide how much you want to charge per sq ft and stick to it for the item, and add this to the cost of the materials.