The cheapest of these plans is $8.33 /month for 1 TB of backup space and support for 10 devices (and three sub accounts), if you pay for a whole year at once. You can add more for the same price and storage, like another 1 TB for another $10 /month. The maximum storage plan you can pay for is 15 TB, but if you want more you can contact their support team.
Digiarty's multi-lingual WinX claims to allow downloads from 300+ sites—including adult sites. Perhaps the biggest selling point of all is the claim that "There is no malware, adware, spyware or virus. 100% clean." The latest version has a much improved interface as well. There are ads, though—on install, I was asked to upgrade to its $29.90 product for Windows and macOS called VideoProc, which does everything that WinX does, but for 1,000+ sites, plus offers some editing for high-end 4K/UHD video.
SaveFrom.net has made a name for itself over the last few years. It can do web-based downloads, but also provides software to install and a browser extension, which it pushes. It doesn't support 4K, but few helper sites do—going to a 1,440MB WebM file is an option, but it doesn't come with audio—the only format that does is 720p MP4s. Nor can you use SaveFrom.net to make an MP3. Of course, those options are in the downloadable software.
Another workaround: Go back to the desktop and try AnyTrans ($39.99 for a single computer), a file manager for iOS devices that has an integrated downloader supporting 900 sites, including YouTube and Facebook. It'll transfer the videos to the iPhone for you over the USB cable. Even if you don't pay for AnyTrans, the download option remains and is free forever.