Honestly, I think most DVD players have them these days. For that matter, many TVs also have a USB port on the back which supports playback, but that varies a lot more between models.
Anything made since around 2012 will have a USB for videos. Anything older and they tended to just be for photos
They do exist. As for deals, I cant help you there, maybe a second hand store
Try your tv if you have one already. My flat screen tv has a USB port, the only issue is it only reads a few levels deep so if the folders or files are nested too deep, they might need to be moved so they are only 1-2 levels deep
Yeah, no problem. I have 3 of these Samsung BD-J5700 players. Found 2 of them at thrift stores, cheap. At one time, I had a hard drive I just left plugged into it with a bunch of shows and downloaded YouTube videos. It worked great. Now, I just have a PC plugged in and my players are just collecting dust. But if you can find one of these, they work great for playing off USB.

Most of the newer players with USB can. Even some TVs as well.
The trick is you’ll need to convert the videos to a compatible format.
The manual will hopefully specify what format it’s expecting. But the mp4 container with h264 video and mp3 audio will likely work on nearly all of them. A tool like IFME can be used to achieve that. https://sourceforge.net/projects/ifme/



