Unfortunately, my Guest post has been deleted, which makes nonsense of my apology for not being logged in.
I was pointing out that the machines Joe refers to are all free-standing instruments with internal sound generators as well as Midi capability.
What is more usual these days is to have a keyboard which is only a controller for sounds generated inside the computer, and which all have USB as standard these days.
These are a few examples
M Audio is a reputable brand. I use several of their devices. They are far cheaper, and sometimes better than a workstation/synthesiser keyboard.
Cheers
Dave

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Sorry 'bout that, Dave. One of the volunteers got carried away. I undeleted the missing posts.
-Joe Offer-