Hey rocknload! There is a difference between the two. I'm not an expert, but from what I understand the 980 is a combed ringspun cotton t-shirt. It has a very soft feel. The 989 uses "soft spun" yarn. They actually take OE yarn (like you would find in your basic t-shirt) and use spinning technology to give it a softer hand than traditional OE tees. The cost difference comes from the cost of using combed ringspun yarn which is much more expensive.
If you want to see the difference for yourself, I would order one of each and wash them a couple of times and see which shirt works best for you.
Hope that helps!
Mindy Anastos
L.A. T Sportswear