I'm making a few assumptions. Assuming single table and 10 players max, you need a minimum of 150 20c and 120 $1 for an enjoyable and playable set. You might be able to get away with 100 20c if you can tolerate the change making, but 150 is a safer minimum. Assuming you want multiples of 20's to make it easier to count with plastic racks, here's one sample breakdown:
160 20c
160 $1
120 $5
60 $20
Total Quantity: 500
Total Bank: $1992
If 500 isn't a limiting factor, you can be more flexible and add more $1s and $5s.