Prime video's would be "free" (other than internet bandwidth). Amazon will also occasionally have free content you can "buy" for $0.00 and add to your library if it's something of interest.
As far as purchasing cable channels there are a few services that offer "skinny bundles" like
SlingTV which runs $20 and up depending (I have Sling Blue and an add-on which is $30). Depends on your cable subscription as to if that's a better deal or not. You can't really buy "al la carte" and just pick up 3 or 4 channels or anything like that. Other options besides services like Sling would be to get something like
Hulu and watch shows "on demand" provided they have content you want (
Hulu does a live TV version for a bunch more $$$). Another sports option, besides something like Sling, is ESPN+ but note that it's like "bonus ESPN" and not regular ESPN.