If you're passionate about continuing to build out the vision of this project, you're probably not going to agree on a number. If you're happy to take a little

If you're passionate about continuing to build out the vision of this project, you're probably not going to agree on a number. If you're happy to take a little cash for it and move on to the next idea, or even if you're not sure about the first point, I would put a reasonable number out there based in some measure on the value of your time in getting it built (ie, the amount of time it would take someone similarly skilled to replicate it), plus some premium. Entrepreneurs always have lots of ideas, so you need to simply decide if this is in some way your "one great idea", or just an "easy come, easy go" etude.