Even if money is no object, if you want to watch bluray-quality 4K content your only choice is to buy the physical media and get it shipped to you (and then use some horrible proprietary player interface). I'm not aware of any streaming services offering the same bit-rates at any cost.
Then you didn't look very hard.
https://www.kaleidescape.com/
There are a couple others as well.
This requires a physical device to be installed on-prem, I'm talking about something you can install as an app, or a website you can visit.
Their tagline is also "Downloaded, Not Streamed"
But if you internet is fast enough, you can still just play it without first downloading it.