What kind of refrigerant oil?

I'm planning to replace the compressor on my 97 GT tomorrow, but I am having trouble locating the correct refrigerant oil. My ford manual calls for "YN-12b" motorcraft oil. In terms of something I can buy at the parts store, what does that convert to?
I see PAG 46, low, medium and high viscosity, but have no idea what to buy. I could go to the ford dealer, but will it cost more than 20$ for a little bottle of oil?
I did a search of the trusty 4.6 forum, but absolutely nothing came up with the key words PAG or YN-12b.

It seems that ester oil is not correct. That's what is commonly used on R12 systems that were converter to 134a because it doesn't mix adversely with the oil in R12 or 134a. It doesn't seem to be correct.

I went to the ford dealer today and purchased the correct ford spec oil. I want to do the job right and not have to do it again! It is definately a PAG oil. The label says "PAG refrigerant compressor oil". The label also says it contains "Polypropylene glycol dimethyl ether", which is definately a PAG oil. The spec rating on this oil matches what my 1997 Ford technical service CD calls for, so I'm certain it is correct. It was slightly expensive at 25$ with tax, but at least I know I got the right one.