*Offer good towards new product purchases only and cannot be used on product renewals. Cannot be used in conjunction with any other offer, sale, discount or promotion. Not applicable to ICANN fees, taxes, transfers, premium domains, premium templates, cloud server plans, WP Premium Support services, any marketing or design services performed by our Professional Web Services team, gift cards or Trademark Holders/Priority Pre-registration or pre-registration fees. After the initial purchase term, discounted products will renew at the then-current renewal list price. Offer may be changed without notice.
The best way to get discounts on renewals is the Discount Domains Club (which discounts domain renewals), but that only is cost effective of you own more than 21 or so domains.
Coupons are meant to bring on new customers and allow them to try new products before deciding on whether or not they want to keep them long term. That being said, goDaddy prices are very reasonable (and no, I do not work for GoDaddy).