There is nothing wrong with belt drives...in fact most low cost machines have to use them in order to achieve plasma speed ranges (between 10 and 300 inches per minute). If you are only cutting materials thicker than 12 ga or so...then 150 ipm is adequate.....thinner and you need more speed and more acceleration for good cut quality.
A full featured height control is critical....it must be able to physically locate the plate serface before each cut cycle, retract to pierce height, then index to cut height...then activate arc voltage feedback (after the cut and motion starts) to maintain accurate height during the cut. I have never seen a 4 x 4 machine with full height control for less than about $7500....as the height control system alone sells for over $2500 (electronics and z axis hardware).
There are the major brands such as Torchmate, PlasmaCam (each has 10's of thousands in the field) as well as a dozen or so smaller companies that produce entry level machines. There also is www.candcnc.com that produce the electronics, software, motors and drives, and height controls at very reasonable prices....build your own machine or purchase from Armstrong Cnc and you can have a machine in the price rang you would like.
Jim Colt Hypertherm