Thanks to scorpiohkg at Reddit for the tip!

You are able to get the FREE Watermelon Beach Towel with less than $25 select sunscreens purchase at Ulta.com!

My example cart:

1. make sure the before discount amount is over $30, like in the following picture $33.98
2. in my cart, add 4 Austrian Gold to the cart to bring up the free towel
3. drop the quantity to 2, total is $19.11, the free towel will stay!