The refill price includes a trigger.
I need to ad one more important point to the ABS pack maintenance. You need to weigh your canister to check that is full, without the cap. You will need a 1000 gram scale to do this. The canister needs to weigh within 5grams of the posted weight on the canister.
If you have a black canister the numbers can wear off the sticker, so write them down for future reference.