Stuff that makes a Fuji and your Scott CR1 Comp great bikes is not that important when adding a motor. Five extra pounds costs you money to lose, but it is nothing for an ebike. And the torque of a "small" 250W hub motor can rip up a carbon frame.

In my opinion, you can only ruin a a nice bike with a motor kit, but you can transform a slow bike into a trusted e-bike. Can you get a used steel frame bike?

What's your speed/distance requirements? For $500, you're looking at around 20 mile range and 14-16 mph.