Either you wait until music city is open and see if it's possible to make money, or you spend your money wisely until your pet is at adult stage.
I would suggest saving your money and only buying meals. The pet evolves to a teen a day after it turned to the toddler, and to an adult a day after the teen.
Then send your pet to school and the rest of the band will evolve and if you start a band, you can do concerts and stuff. The next day, you should receive money in the mail. (First day I got 2 million GP, the next 5 million)