I don't know what you are thinking as far as motor/battery/controller, but the MSRP on that stuff is ridiculous for the "Big Four" (Shimano, Bosch, Yamaha, Brose). For example, the 500WH battery for Bosch is $900, the motor is $1100, the controller and associated stuff will set you back around $500.
For a mid-drive, the frame has to be built to match the motor. Kinesis lists them in their catalog, but they don't sell to individuals, only OEMs.