There is a legal hurdle there. Copyright and many boilerplate terms-of-service completely forbid automated polling. If you're building it for yourself, that's probably not going to raise any eyebrows but if you're flogging access to it, the original content owner might start to care.
But assuming it's legal and with permission - that does rather depend on the API. I can't think of any API that I would pay anything than a few pennies for.