I buy oil in bulk, not "shock oil" mind you, but that is the key to getting a better price for me. If you can find a comparable oil that has the proper qualities and can purchase in a 55 gal barrel or larger, will cost more up front, but save in the long run.
Call AAron at ORW Temecula, I would tell you but forgot the make of it, same oil as Fox red with out the color I have run it with no issues and saved a lot I do all my own shocks and have the same oil we started the year with. I threw the bottles away but I think its Torco motorcycle shock oil but check with him
Tellus T-22 is what King uses in most of their shocks. I used T-15 in Harley Shocks for a long time so I am very familiar with their oil. Tellus oils are OK, but there are a lot better choices out there.
Fox JM92 oil is the best, and worth the money:
It has the highest VI rating meaning it won't fade as quickly
It seems to do well with friction (I haven't done a back to back for comparison, but Fox in general does well here)
It has the highest temperature rating
There are some more specific numbers on the Fox vs King article on my site.
I always recommend people use the original manufacturers oil, it has been tested and proven to work with their construction in tough conditions. Nothing is worse than running a cheap oil only to find out it didn't lubricate properly and caused a leaky IFP.
If you really do want to save a few bucks and don't have high performance/durability requirements then ATF is a common choice.