There are never deals on Costco memberships. But there is one loophole. If you know someone with an existing membership and you want to pre-pay for your purchases in advance, you can have them buy you a Costco Gift Card.
You don't need a membership to use the card, but you can only spend up to the amount on the card.
(Ignore any older articles on websites that say differently. Once upon a time, if you started with a $5 gift card balance, you could do a hundred dollar shopping order and add the remaining balance in cash. This allowed you to avoid ever needing a membership. But this has changed. They will ask you right at the start how much the balance on the card is, and limit your purchase to that amount.)