The sensors were $50 each and the gateway is $100, you can use them without the gateway but you have to be within bluetooth range. The gateway has a bluetooth receiver and acts as a wifi gateway. Once the gateway is setup you can disable bluetooth as you can read everything across your wifi network and then anywhere as their cloud service is free.
If you look at my post here
https://www.rollitup.org/t/diy-with-quantum-boards.927159/page-219#post-13573647 you can see the little blue and green square sensor hanging from a string in the middle of the tent.