Good question. For two years i have been trying to figure it out, before because i wanted to colloect more for my self most of my co worker orders and i name the price and they dont complain then i sticked with one price after that asking them it dependes in the size, now recently i price my work per square inch, i charge 50 cents per square inch and seems resonable then if its too much input it down to 45 cents or 40 cents. I dont have much artwork at home due to orders from co worker but its ok cause i buy more supplies and some bitcoin for my sales. Never put your price down, if not raise it up more, its gives it more value to collectors. I gove some for free for patients and special friends, families and for gifts