Artists

https://graphicartistsguild.org/product/the-graphic-artists-guild-handbook-pricing-ethical-guidelines/

Selling an original is one thing (and one price) reproduction rights are another.
This will confuse some clients who have not dealt with the difference and they sometimes balk.

You'd want to know how many items the image would be used for, would the client want to offer you a royalty per item? Or pay a flat fee for all (or limited) rights?

It can be tricky, most artists sell themselves short and are frankly just happy to have a buyer.
Don't do that.

But bear in mind that an image may have extended value, like signing on with a stock image catalog for instance.

I'd suggest calculating a price for the original, (figure a minimum for your time, materials and skill per square inch, this often makes it easy) add more for the repro rights and offer the buyer "exclusive" rights allowing them to reproduce it any way they wish for the total. You need not explain how you got to that price.
Remember to retain the right for use in self promotion in your portfolio if you sell all the rights.

And stipulate that you get a copy of anything they print your image on. You'd be amazed how many will commission a piece of art and sign their own name to it.