What is the value of a red skelton signed photograph?

Very little. Prints that were selling for $1000 in the 90s can be found for $200 on eBay (do an advanced eBay search and select completed auctions, the order by price). They were over produced and the market is flooded. The best you can hope is that he gets more popular and the poorly produced lithographs begin dying off. I do not foresee this happening. If I were you, I would get what you can while you still can.