Sagging skin due to long-term prednisone use, what are my treatment options?

Make sure you coordinate care with you plastic surgeon and rheumatologist/immunologist. With your history, you have to be very upfront with your plastic surgeon and other MD's.
The biggest problem would be wound healing, especially since you have been on extended prednisone treatments for many years. This will "thin" the skin/dermis and decrease your normal wound healing. 
Start taking your homeopathic medicines, such as Vitamin C, pre-op Vitamedica and others that will help healing. Good luck! 

Prednisone is sometimes used for the treatment of chronic immunologic disorders. It can be very effective but also has some very bad side effects, especially to bones, skin and conective tissue. It basically decreases the body's normal construction of new collagen and other building blocks to support bone and skin. It also decreases the body's ability to fight infection. Surgery, including facelift surgery can safely be done in patients who have been on Prednisone in the past bas well as patients who need to continue taking Prenisone. It is important to tell your surgeon that you are taking Prednisone in order to prepare you properly both before and after the surgery. Good luck.

There are much better options for facial laxity for patients in their 30's than previous years.  Facetite (RF delivered underneath the skin) is an option, as is combination facial fillers and laser resurfacing.  Often times laxity can be a result of volume loss.  It is unusual for a patient in their early 30's to have a facelift.  Best Dr. Anil Shah

it doesn't sound like a non surgical treatment will do you any good.  You sound too young for a facelift but I have occasionally performed this in someone your age.  You say your eyelids are an issue.  You might want to start with an eyelid lift.  It can be done under local anesthesia and the recovery isn't bad at all.  Not a bad option to begin with.

 My recommendation would be to first talk with your medical Doctor who is treating you for your lupus to see whether it is safe for you to undergo surgery of this type. Second, you need an in person consultation and examination with a board-certified plastic surgeon  Who can examine your tissues and help you understand what can be achieved, short term and long term.  Only after examining the integrity and quality of your skin could one give a valid recommendation as to what could be accomplished and your likely result.   Best wishes.