Sorry for our late reply.
For the product button modification:
We think $100 is impossible. We discussed with our developers, then they said they can't do that modification with $100.
Their minimum price is $180. So if you can pay this, we will contact our developers again.
And for your founded solution.
It is impossible. You can't edit the product special area with elementor builder.
If you use elementor pro version, you can create your custom product template.
But in that case, you need to build all product page layout with elementor pro template.
You never edit the red marked special area with elementor. It's really impossible.
And if you make the new product template with elementor pro, it will be more harder than parent theme modification,
Anyway, please consider more details and choose any one.
If you have any other questions, please let us know again without hesitation.
Best Regards, C-Themes