Mozart made a lot of money, and lived a somewhat extravagant life. But he was also swimming in debt as a result of poor money management and various circumstances somewhat out of his control. I answered a similar question about his finances about a year ago, the gist of which is that while he had some periods with a lot of cash flow, he had lean years as well, and didn't necessarily budget or save wisely. It didn't help that he spent most of his time surrounded by wealthy royals and aristocrats, so he developed a pretty expensive taste in clothing.

Also, weren't artists sponsored by the King or something? How would one go about it? Create something, go to the castle, show it to the King and ask him for a pension?