The first drive I made was just to personally see the limits if the design, and evaluate if there was a market for them, The second one was functionally identical, but slightly different to make it more professional-looking (all fasteners are metric, used steel rivnuts instead of tapping threads into aluminum, shifted position of the motor one inch to ease access to mounting-plate connectors, etc). Since I have firmly decided to not make these for sale, the first drive is collecting dust and I would be willing to sell it for the cost of parts (It was fun to make, I'm throwing in my work for free).
If you follow the build-thread, you would be getting the drive on page 5, you can compare to the one I'm keeping which is on page 6. I'll figure out what the price would be (no obligation to buy). It sounds like you would be best served by a 6S/22V system, the remaining question is what Kv of motor and diameter of roller would you like? I only have one 295-Kv motor, and a 250-Kv that have shafts cut to fit the slotted roller-tip. If you want to buy a motor with a different Kv, I can sell you a slotted shaft you can swap-in.
My interest right now is the MAC axle-to-driven-shaft conversion that crossbreak is doing. I believe it is an important development, and it can be used as a left-side-drive, or a BB-drive similar to the GNG (but capable of much higher wattage).
edit:
$35 stem and seat-post tubing shim
$90 Castle Creations Phoenix ICE 75A ESC, plus two extra 50V capacitors
$10 servo tester + servo wire (used as a throttle)
$80 Exceed 63mm 295-Kv motor with notched shaft tip
$85 Copy of EVTodd drive with 1.5-inch roller
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$300
Does not include battery or charger, I could sell you this LiPo charging set for $80 ($40 25A power supply, and $40 10A 6S charger). There are better/faster charging systems, but I consider this set the minimum I would recommend.
http://endless-sphere.com/forums/viewtopic.php?f=16&t=23465#p341300
beaversSuck has first dibs on this kit at this price, but if he passes on it, anyone can buy it. Be aware if you want to upgrade to a higher voltage than 6S, you will need a different ESC and charger. I got 20-MPH using 24V and a 1.25-inch roller, 22V with a 1.5-inch roller might get you 23-MPH.
If you want to get a higher speed than 23-MPH with 1.5-inch roller at 6S, you will need a higher Kv motor. The smaller 50mm motors have higher Kvs, but less leverage, and less copper mass to absorb/dissipate heat. EVTodd was happy with the 50mm motors on fairly level ground, but he was using 37V.
This drive system works great using a 63mm motor at 36V-44V, but when you add the extra costs of the higher voltage battery/charger/ESC, a GNG or cell_man geared-hub looks pretty good. The one big benefit of this drive is that you can lift off the seat and carry the drive indoors/upstairs while the bike stays down at the bike rack.