For gallery Prints consider this

Gallery will take 50 % you will be required in most cases to provide image and frame.

If you are selling a image in a 30 x40 frame for $1500

then you will recieve $750

minus the cost of print and frame lets be super conservative and say $300

therefore the gallery recieves $750 - they handle the rented space, marketing and bring the client list
you recieve $450 - supplying the framed pieces

If you do not like this arrangement of funds up the price of your work and do the math.