Since your intention is to sell them, I suggest researching what similar items have actually sold for on eBay, and price them accordingly.
Before photographing them, I would give them a bath in a mild soap and water solution, wiping grime away with a soft cloth or swabs. Rinse in fresh water, and lay them on a towel to dry (the silk needs time to dry.)
Paying for someone else to restring them would probably not be cost effective, but selling them unstrung would limit your buyers to people who are willing to restring them.
If you wish to restring them yourself, it's not hard, and it doesn't cost much (especially since you already have the clasp)-- thread, needles and gimp (French wire) are inexpensive and you don't need special tools. We have a tutorial and videos on the Lowly Beaders Forum and there are also stringing videos on YouTube. Wash the pearls prior to restringing.