Here are a few things to keep in mind if you want decent plasma cuts:
-Speed range is critical. There are quite a few low cost machines on the market (from major suppliers even) that have an upper speed limit of 150 inches per minute.....above that speed they become extremely unstable. Plasma is a speed dependant process. On 1" steel with an 85 amp plasma you may be cutting at 20 inches per minute, yet a few minutes later you may need to cut some 18 gauge.....which cuts best at over 300 inches per minute.
-Acceleration capability at all speed ranges is critical. When cutting thick material it is relatively easy to accelerate to full speed almost instantly as your full speed likely is rather slow (example above of 20 inches per minute on 1" steel). Acceleration is also very important at high speeds....think about having to cut fine details and small holes when cutting thin material at over 200 ipm. Most low cost machines....or at least machines with poor acceleration or improperly sized drives will never come close to the speed required to get best cut quality on fine features. Incorrect speed changes the cut quality. Wider kerf, heavy dross, thicker heat affected zone, poor edge angularity and material warpage are all by products off poor acceleration. Some of the major brand industrial cnc controls allow you to have more than one set of acceleration and drive tuning parameters based on speed ranges......this allows you to fine tune the drive parameters to get best performance i different speed ranges. I have not seen any of the low cost systems with this capability.
-I hear lots of complaints about these lightweight, entry level machines.....but keep in mind that light weight moving parts contributes to the machines ability to accelerate. Too flimsy and you will get mechanical flex and vibrations that affect cut quality, too heavy and it is difficult to get to speed. I have been working with high end, heavy duty industrial cnc plasma maniufacturers for over 30 years. Some of todays heavy industrial machines with 30' wide gantries have an amazing ability to accelerate and follow accurate cut paths even at high speeds......they are expensive...generally well over $120k for a small 12 x 20 machine, and a few hundred thousand for a large machine. I have a $12k PlasmaCam in my home shop that cuts very well, has excellent acceleration and the ability to cut at 400 ipm.....it has a very lightweight gantry and carriage and servo drives. It is no comparison to industrial quality machines in terms of how it would hold up under high production use, but for my hobbyist use it is a perfect machine.
-Height control. Pierce height needs to be accurate and 100% repeatable. One pierce too close on material thicknesses over 3/16" and you will damage the nozzle orifice, once the orifice has even a microscopic nick....expect varying cut angularity. Cut height needs to be accurate to plus or minus .005" of the plasma torch manufacturers suggested height while cutting. The torch height control needs to be intimately tied to the cnc to ensure that the height remains constant and correct during slowdown for cornering and fine features and during kerf crossing.
-Software. CAD is pretty universal, better CAD drawing programs will make you more efficient at drawing parts, there are many variations based on specific needs be the drawings artistic or geometric in nature. CAM in its simplest form inputs the CAD drawing file and applies lead ins, lead outs, cut directions and kerf compensation. It then generates the machine code that is sent to the machine control software (like Mach3, or a few others). More complex CAM can load cutting configurations such as speed, amperage, arc voltage [pierce height and a few dozen others.....makingthe processes less operator dependant, and more sophisticated CAM actually ties into large companies inventory systems to track and monitor plate inventory and remnants, as well as doing geometric nesting of odd shape parts and supllying cut cost and plate utilization reports.
So, don't just build the heaviest machine you can build so it will last forever, make sure you take into account the motion control needs of the plasma cutting process. heavier machines means larger, inertia matched drives in order to make a large machine perform as well as a small, light machine.
Jim Colt Hypertherm
Well, if you are I am too 
I'm about 1/2 way finished with mine. 
