Of course, adding on more bags will increase the total price, but you also need to consider UNIT PRICE. If you are able to get 5,000 bags for $1,000 and 7,500 bags for $1,100, the unit price becomes 20 cents per bag and 14.6 cents per bag, respectively.
If you are launching a new product, or perhaps a new company, you will have less direct experience with how your product will sell. Ordering might become a trade-off between the quantity discount and your concerns about using all the bags you order.