A design contract stated that work done would be for the cost of (1) final presentation folder design. Upon presenting three concepts to the client for consideration (concept 1&2 being similar and concept 3 being significantly different), they've decided they now want to use both concepts 1 & 3 to have two different folders.
I am trying to determine how I should charge for the license to use this additional design (#3) that is significantly different from concept 1. Just because concept 3 took me less time to create since it was based off some similarities to concept 1 shouldn't meant that its value is strictly based on those hours since the client will have double the benefit of a second folder for their marketing.
I'd appreciate anyone's thoughts on this matter.