I doubt if it's ATF as so many tight ******* are forced to buy it that if there was good reason to think there was a cheaper alternative they'd be using it!
I think it's a case of bite the bullet and accept you're getting shafted.
It only requires top up at present but I'm keeping my options open for the next time I decide to change it. It looks and smells like ATF but I knew there would be a catch.
As others have suggested, you don't need to buy it from case, a lot of other oil companies will have made their versions of hytran to an equal or better spec and usually a lot cheaper. Try an agricultural machinery dealer, oil distributors or some motor factors stock tractor oils.
I've got some hytran you could have had if nearer. There are substitutes, but tbh last time we had a case it was just as cheap to buy as utto was, about 60 quid a 20l barrel