The amount of coins you get per day is based off of how many you have. Without paying for a brokerage account, the interest rate's only 1%. So if you have 100K coins, you get around 1000 coins plus whatever your peeps' salaries are.
The best way I've found to make coins without paying is to sell collectibles and furniture. I only buy things on sale and the 20 coin groceries, and after 10-20 generations I have 200K coins.
I eventually caved and bought a couple brokerage accounts from the store because I was impatient xD If you're willing to pay $2 then they're worth the investment. They increase your interest rate so you earn tons more than normal, and you can get up to 11% of your balance per day. Imho, they're better than just buying coins or any of the other upgrades