Go on EBAY and try to find a vintage motor that is either rebuilt or needs rebuilt. The vintage motors are far more reliable and lots of parts are still available. The vintage motors are magneto and don't need the expensive modules [CDI, AC/DC relay, Regulator, coil, flasher, etc.] and wiring harness to work. The vintage motors have a lot of torque and the clutch system actually works correctly, whereas the new edition motors have a lot of EXPENSIVE clutch issues.
If you elect to use the new edition motor, you will need to do a few upgrade to keep them working , and normally the upgrades are more costly than rebuilding a vintage Whizzer motor.
Average cost to rebuild a vintage motor is approx $400.00 [new seal, bearings, piston, rings, gaskets, labor, etc]. The new edition motor will need the cylinder and head upgraded to make them reliable, and with the labor, and parts will also cost approx $400.00 to make them work correctly. The vintage motor will gain value with time, whereas the new motors will continue to lose value for many years to come.
Hope this information is helpful.
Have fun,