I've seen a number of USB headsets, and any brand name model should give good service. The majority of USB handsets are the type meant to be used with services such as Skype and contain a keypad, which would not be of use with the 3CX phone. There are some "travel" handsets but most tend to have the mic/headset connectors.
I would tend to think that the majority of computer users would want to keep their hands free, and use a headset.
Just remember that you get what you pay for, so anything "cheap" may mean a sacrifice in audio quality.