I also thought about this question for a long time. I knew from using my friend's Grizzly and his KMG that I wanted variable speed. I chose Polar Bear Forge's GIB. I figured if I couldn't put that together I was kidding myself thinking that I could make a decent knife. Anyway, I'm very happy with my choice. But it was a learning experience since I'd never tapped a hole or worked with metal much. All in all, the kit is forgiving. My build survived a broken tap and a few less than straight taps.
As far as costs go, I purchased all the wheels from Beaumont. I forgot what they cost, but the prices are on the web site. I purchased the KBAC variable speed drive, same as is on the Beaumont KMG, for about $400.00 from, I believe it was Statewide Electric. I bought a "new" 3400 rpm 3 phase 1 1/2 hp Baldor on ebay for $125.00 and could have done much better. Recently a couple of "new" 2 hp Baldors sold for less than $ 70.00. I bought the 1 1/2 hp and KBAC drive because I thought I would be a using 120 volt line, but found that the wire wasn't the right gage for the motor so I ended up using 240 volt. If you know you will use 240 volt you can probably get a less expensive drive. Part of the cost of the KBAC is that it allows the use of 120 volt single phase input (for a 1 1/2 hp motor) or 240 volt current for up to a 2 hp motor.
I used typical hardware store taps and drill bits. The steel is pretty soft. A decent drill press (I used a benchtop Delta) and drill press vice are helpful. I bought the tension springs from the local hardware store as with all the bolts and screws, but be prepared for a few trips. The biggest hassle was finding the cord, plug and glands for the motor, VFD. But that's because I had know idea what I was doing. At any rate, the "project" took a while. But after having made one I could make another easily in a weekend.