https://www.rei.com/membership/join
I have been a member since around about 1964 and very happy. Well worth the expense - it will be returned many times over.
@Gary1 yes, there is a one-time $20 fee to join the co-op and you can join online or in-store. Co-op membership includes a bunch of perks (a few examples: annual dividend, special offers, access to Garage Sales, and discounts on classes, rental and services); you can learn more here. Hope you'll join us!