Trying to figure out how much it would cost the customer to develop the same functionality is probably the best strategy (and suggested by most posters in this

Trying to figure out how much it would cost the customer to develop the same functionality is probably the best strategy (and suggested by most posters in this thread). I would add that the customer may not come up with a detailed estimate/calculation so it's more a question of how expensive they perceive their development costs to be. (If their developer casually says, "I can do this in two days", that's bad even if it's wrong.) One probably has to factor in the (possible) inefficiency of the customer, i.e. inexperienced devs and the usual overhead of working at a large company. At first, I thought that by cutting the costs in half, you would end up with a fairly low price. But giving them the option to receive the source code at double the price is a nice touch, especially since you say most of your customers want that anyway.