Size of the market is also important. Text editor for 30€ is a good business, everyone needs a text editor. Database client for 30€ is probably a little less

Size of the market is also important. Text editor for 30€ is a good business, everyone needs a text editor. Database client for 30€ is probably a little less profitable, not as many people need that. Client for a specific database like the protein data bank for 30€ -- well, you might sell two or three copies. All of these are probably a similar amount of work, but you can't sell them for the same price. That being said, a menu bar widget has such a huge market that I don't see why they are pricing it so high.