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 R$ 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). In this example (10 x 20) x (5) = R$ 1,120 should be your minimum budget..
Avoid creating low budgets (less than R$ 500) for deep discount coupons such as 80% off or R$ 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.