An efficient budget covers the cost of the customer demand that your coupon generates, for the duration that you set. For example, if a product is selling an average of 20 units per day without a coupon, and you want to run a $5 off coupon for 10 days for this product, the minimum budget you set should be: (number of days x number of average daily units) x (discount amount + redemption fee). In this example (10 x 20) x (5.60). $1,120 should be your minimum budget.
Avoid creating low budgets (less than $500) for deep discount coupons such as 80% off or $35 off. Low budgets for high discounts will cause your budget to expire rapidly in a couple of hours. As a result, only a handful of customers will be able to see and interact with your coupon.