Definitely a +1 on this. If they want it badly enough, they'll pay. And then to clear your conscience, you can always donate to the project with your newfound riches.

Honstly, if the code is BSD licensed, the only reason they want you to do this is to get rid of competition for their own benefit, which makes them undeserving of a generous price for your time and reputation. It's not like the BSD license would restrict them from using your project anyway, even for commercial purposes.