Before you do anything, make sure that it is not the oil pressure gauge line that has blown. It would not be a welcome surprise to discover that it wasn't hydraulic fluid, but engine oil. The hydraulic system can survive being run low, but running out of engine oil will pretty much relegate the tractor to the scrap heap, as overhauling the engine will far exceed the value of another good running tractor.

Non-Synthetic Hytran "Premium" (it's new name, corresponding to a change to a different supplier) is only about $80 for a 5 gallon bucket from the dealer. Much cheaper than the previous product. You must have been looking at the full synthetic which is much more expensive.

Is it important to use it? Sounds like you've already made your mind up, so it isn't important to you.

There are plenty of "hytran compatible" products on the market at much cheaper prices. At the very least I would recommend choosing one of these. It will either list CaseIH Hytran as a compatible fluid, or it will list the MS-1209 spec.