Regarding this, what does REI membership get you?
Members receive 10% off of almost everything in the store automatically (paid back in an annual dividend), access to members-only deals, deep discounts on REI classes, events, and adventures, and can vote on the company's board of directors, among other perks.
Beside above, why is Rei so expensive? REI primarily sells high quality name brand equipment at competitive prices. They provide a 10% annual dividend / rebate on regular price items. They also have a return policy that allows you to actually use the items in real life and if it doesn't work like you want you can return it for refund or replacement.
In this manner, can you shop at REI without a membership?
Yes, you can. You don't have to be a member to purchase, but your membership fee goes towards your local state parks, county parks, and national parks. I would suggest a membership if you plan on buying anything over $200 retail price, not sale or clearance.
Can family members use REI membership?
Other family members can use your member number to earn a member dividend, but the membership can't be transferred to someone else. Your member dividend is based on eligible purchases, which exclude REI Garage items, discounted items, gift cards, REI Adventures trips and services.