The short answer to your question is "Yes!" Injectable hyaluronic acid-based skin boosters have been used successfully for treating sagging elbows, saggy knees, and even saggy upper arms. Skin boosters work by promoting new collagen and elastic fiber synthesis to improve the quality and smoothness of the skin by enhancing hydration and promoting greater elasticity. In the U.S., we do not as yet have specific skin booster injectables available. For this reason in my NY office, I typically use Restylane Silk for this purpose. In my Israel satellite facility, where a far greater number of dedicated skin booster products are available, I typically use Viscoderm Hydroboosters, Profhilo, Juvederm Volite and Restylane Skinboosters. As to how much it costs, that will depend upon the experience and location of your physician and the particular material or combination of materials and amounts needed to get the job done. Be sure to consult with an experienced board certified aesthetic physician, since this location is not for novice injectors accustomed to injecting simple Juvederm or plain Restylane into smile lines. Best of luck.