http://www.autozone.com/N,14600949/shopping/partTypeResultSet.htm

I have an 85 300td.

I searched for power steering filters on a few auto supply store websites and have gotten a lot of different products.
In the above link, there are two products that came up. There is a cheap ($2.00) filter, and then the $20.00 filter. The $20.00 filter is what matches the item listed on the Parts section of this website.
I was curious if the other product is just a cartridge that I could use to replace the old cartridge, or do I need to buy the whole, more expensive assembly?
What makes me curious is that on two different company's websites, the $2.00 filter came up as the power steering filter for 85 300td.
What gives?