Depends on which product you are interested in...
Pavlok 3 Pro
Apple Watch Clip
Go to http://pavlok.com/challenge.
After you read click on "sign up now".
You will see a cheaper price in your cart.
Then you can remove the full price one.
Here's the trick to opt out of the challenge you only Pay $100 so that's a total of $150 ish if you cancel within 42 days.
Or you can Pay full price if that's too much hassle for you.