Yea same here, with the truck cost already...lol...and having a smartphone with way better always updating free apps, not much of a decision after using my family's LTZ GM NAVs let alone in-motion.
The prices very by what inputs to the MyLink you may need or desire for the future.
Cheapest way is if you already have the GM A/V inputs. My truck didn't, so I had to do that, then decide on the type of device A/V inputs. I needed HDMI and opted for the cable thou wireless is easy, I didn't want RF issues or limited bandwidth using 1080p vids. The MyLink interface I have has 2 more inputs and also a additional camera input so it is a bit overkill for now but it is cheaper having the options instead of replacing interfaces later to add more.
When the admins unlock the install guide thread the full guide will help you do it, or perhaps decide what system you may want. I went with one from MVI after reviewing different brands and dealers.