Build your own. I have built 5 or more in the past 6 months. No Weld Grinder/Sander or NWGS plans will cost you $25 on the internet. The material to make the frame will cost you about $50. I weld my frames so there is no need to clamp it together. To get the machine ready to grind you will spend about $340 on a drive shaft, bearings, drive wheel, tracking wheel, and a contact wheel. Then the veriable speed motor issue comes to play. I looked a that option and thought "Self, that is just too much money to spend right now. Two 4 step pullies will get me started." And I would not change a thing now! The two pullies will cost you about $30 vs. the $800 for a veriable speed motor and controler.
The only complicated part of building this NWGS is the tracking knuckle. Once you figure out that you turn the piece upside down and use a piece of 3/8 inch flat stock for a spacer and a piece of say 1/4 inch stock a clamping surface, you can weld the tabs in place with extream percision.
Don't be afraid to build your own equipment. I find making my own equipment has been as much fun as learning how to make the knives.....