I have a site that gets ~12 visitors/day and I make about $55/mo through that site all from the Amazon Associates program.

Referring someone through an Amazon link doesn't just credit you if they purchase that product you linked to - it credits you for any purchases they make during the cookied period. And for the whole amount of the checkout.

A couple months ago I made over $150 with that same amount of traffic because someone bought a MacBook Air (~$50 in commission), some fancy espresso maker (~$20) and a bunch of other things. Amazon has mastered the art of the upsell.