Just checked how much I’ve spent on Amazon last year. It was about $4500. Cost of Prime is 2.7% of that. Most purchases were more than $35 anyway. Maybe I’ll pass on it for the next year. $10/mo is a significant psychological barrier for me.
If you spend that much on Amazon you should look into their 5% back credit card. There is an inherent "annual fee" in that it requires a prime membership, but you spent enough that it would more than pay for itself.