I'll make this real simple for you.

Usually the best deals are found when you buy a camera that has a lens or two with it and maybe some extras.

Used monorails are often sold with 210mm f/5.6 lenses because they were extremely popular with the Pro's who needed large image circles for product photography where they needed plenty of camera movements.

A 210mm lens is considered a long normal lens and is perhaps the most versatile of all focal lengths on a 4x5 camera. You can use it for portraits, landscape, architecture and still lifes. They are inexpensive today due to there being a ton of them out there since the Pro's have gone digital. I have seen nice examples sell on Ebay for $150.00 to $200.00.

Any Schneider, Rodenstock, Nikkor, or Fujinon 210mm f/5.6 lens in a Copal shutter will be fine. There are subtle differences between the makes but don't worry about it. You don't know enough yet to be picky.