In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
As a rule I always have an air scoop as well as an expansion tank. Even though the delta T of the systems normally shouldn't be that great to cause much expansion/contraction of the water, and the HDPE pipe (you are using geo-exchange rated HDPE pipe right?) does have some ability to expand under pressure, why run on the edge? Also the HDPE pipe is not an oxygen barrier material, and can get air in it over time. And the last thing you need after a few years are some airlocked loops, depending on how much flow you are using.