How can I make an autoclicker for a third-party site?

Question

JavaScript

I'm wondering if it is possible and is it even possible to make an autoclicker for such a site as, for example , https://relay.amazon.com? The bottom line is that the "order" button must be pressed after a certain price (for example, 1000 rubles) appears on the product. Is it possible to somehow track changes through the HTML DOM? Or is it impossible to do without an API at all? I suppose some kind of script should be attached to the button ID and be clicked from the outside after a predefined number in the script appears in a certain DIV field (500 for example).

I would like to know the opinion of experts.
Thanks