At the $3 tip per delivery you cite, that's 133-167 deliveries. It's not improbable that the all-in cost of driving is $1+ per delivery, also tips of more than $20/month are taxed (at the full value of the tips) for both income and payroll tax (unlike, incidentally, mileage reimbursement up to the IRS limit of $0.58/mile which is completely tax free.)
