Really? Mine have way more money than they need.
Let some money sit in the bank and collect interest. The more you leave in there, the faster it grows. Stop buying stuff as soon as you can barely afford it. They don't NEED upgrades, and the little things (left side of the shop) don't cost much. When you get into your second generation you'll have lots of money and can get the upgrades.
I'm in the middle of my 2nd generation and have over $40,000 in the bank and have upgraded the kitchen fully.
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Runners... never enough runners....