Costco has 81M members or so, at $50/yr that is around $4B/yr total in membership revenue. Their profit in the last year was $2.3B. Thus you are correct, Cost

Costco has 81M members or so, at $50/yr that is around $4B/yr total in membership revenue. Their profit in the last year was $2.3B. Thus you are correct, Costco would lose money if they didn't charge membership fees. Costco's profit is actually really low. $115B in sales with $2.3B in net income, so ~2% profit margin. I guess they really do have low prices. Walmart for comparison has a 3.3% profit margin in the last year on $445B in sales. Amazon has a -0.3% profit margin on $88B of sales.