Apex wants you to buy the whole kit, there were issues with the polymer and Aluminum trigger not working properly due to the sear/trigger geometry. Do a search here, there is a thread with a member who went through this and he had to buy the "2-dot sear" and it worked perfect. Another member was able to use just the poly trigger, but he had to "shave/deburr" part of the poly trigger to make it work properly.
Many of us have bought the aluminum #100-064 trigger and it is a perfect drop-in IF you also buy the "2-dot" sear to go with it (#100-063). Will be the same with the equivilant Poly trigger only (#100-025). Just get the apex 2-dot sear, it is worth the $38 dollars for a custom machined, hardened part (not MIM), pay once, cry once.
You are not going to save a bunch of money by buying just the trigger and sear separately. But Brownells sells the "2-dot" sear for $38 or so, and the poly trigger can be had on ebay or elsewhere for around $35-$40. (I would just bite the bullet and get the AU trigger for $70)
I don't know how much the kit goes for, but it is not needed in my opinion. The trigger and sear only, brought my pull weight down to 4lbs. but still has kind-of a long take-up, which I don't mind. This is with the "stock" sear spring. The trigger comes with a heavier sear spring which will up the trigger pull weight a bit, but I did not use it.
For reference the #100-126 is the poly KIT. The #100-179 is the Aluminum KIT. The #100-064 is the Aluminum trigger only. The #100-025 is the poly trigger only. The #100-063 is the 2-dot sear. These are all the parts that will work with the 2.0 compacts. You can save $20 bucks or so by just buying the trigger and sear if you shop around. I used the AU trigger and the 2-dot sear and nothing else...works PERFECT, looks awesome, and no failures with HST's, Golden Sabers, Hydro-shocks, Ranger's, and ball.