Maria, your art is delightful. I understand there are 26 cards and that they are all the same size. To price the cards we have to know their usages. When you are creating something to be reproduced you are transferring rights to the publisher. So what rights are you transferring? Where will the cards be distributed, how many will be printed. Are you selling the original art? Is there a booklet included with the cards. A box? Were you commissioned to make the cards for someone else? What was your agreement? Are you working on a project for yourself? Will this be a Kickstarter campaign? So many more questions all having to do with what the cards will be used for, who is publishing them and how they will be distributed. Honestly, once you have the answers to these kinds of questions, you may actually find the answer to how you want to price them.