Its designed to attach the prop of a model aircraft directly, i.e its designed to drive a fan that cools it. It has little (or none) weather protect, and would be destroyed on a bike in months. Another concern I would have with that motor is the shaft size- its one thing to deliver 2000W to a prop, but to connecting it to a mechanical drive train that can load it with sudden changes in forces is likely to destroy it, you would need to get very creative with shock isolation from the drive line.
As far as costs, I doubt the basic motor part of the bike kit costs all that much more, after all, its only a few coils, a shaft and bearings.
The very best current commercial mountain bikes come, despite a lot of frame design and engineering, with a a huge, ugly and heavy mid drive motor. With all the R&D, and money to be made creating the perfect E-Bike, do you honestly think if the big boys could add a 2000W motor weighing 670gram and the size of a bottom bracket, they would not have done it already?
As far as battery packs, with the right controller you can roll your own easliy enough.