How high should our license fees be?

After we spent time and money developing several software products, we have decided to focus on one customer group and to promote just one particular solution which is going well so far. However, we'd like to not let the other projects go to waste. Now if we license out the software, how can we make sure we're asking for an appropriate license fee? Should we consider the working hours that went into the software (= complexity/difficulty)? We don't just want to ask customers what they are willing to pay.