Seems that I managed to get in contact with the person who wrote this module in the end. He could tell me that he doesn't support it any more, nor does he know anyone else who does. For all intents and purposes therefore, it looks like this module is dead. Too bad, because the idea is good, had it only worked correctly. The way it is now, apparently workiing but giving prices that are totally off, it is not exactly good for business.