How much should we charge for an Exclusive Design on a handmade,custom soap?

I own a small Natural, Handmade Bath and Body business. We sell to hotel shops, souvenir shops and small boutiques, including pet shops (only our pet products of course) and occasionally we get a custom soap request. According to the store, we design a soap exclusively for them.

How much should that exclusive design fee be? I make it so it expires in 1 year and they have to renew and usually charge a one-time fee of $50. Is that okay?

Thank you!
V.L.

You can set price for your one working hour. Now you can calculate how much hours it takes to make this custom design and you get the price.