if you don't mind the trouble, you should apply for the Executive membership, which is the 100 dollar one.

For Executive card, At the end of the year (anniversary date), costco will calculate your rebate and issue you a rebate check. If your rebate check is less than 50 dollars, you can go to membership service and ask to exchange the rebate check for $50 refund on your membership fee, that results the same as if you pay the $50 membership fee.  If your rebate is over 50 dollar, then you use the rebate check towards any purchase in Costco.

Only Executive card gives you 2% costco rebate.

True earning AMEX card will give you other rebates like people said in above.