For movies and series, there's a process called "Minimum Commit" where the media companies have to commit to spend $X for a bundle of content that includes both the content you want to sell and a random selection of crap to pad out the offering. Then it depends on the deal, but often the amount that each item is watched then contributes to the royalties cost. The relative exclusivity you might want will then dictate the overall cost and royalties returned.

For sports it's different, typically you bid for the right to own a geographic market and the games are sometimes split into bundles where you can bid for one or all bundles depending on how deep your pockets are. You'll then get to keep exclusive or non-exclusive rights for a certain number of years. You'll then pay annually/quarterly for that right at the total bid package for the term of the deal (e.g. 5 years). Depending on the contract you might be able to re-sell that right to other companies as well, which dilutes your audience, but may increase the distribution overall.

Then aside from the rights, you end up paying infrastructure costs both fixed and variable. You also generally commit to CDN capacity for distribution based on a forecast of how much you think your customers will watch in any quarter.