well, you can assemble the kits yourself from parts online, and that works great. ebike motors are super simple and there are millions of vendors all selling the same grade equipment.
1500USD is quite a bit above what a normal DIY costs, but with a crank mounted motor dumping twice the legal limit wattage output into a cassette via a bike chain, it became nessesary to swap a lot of parts and that figure includes the frame, wheels, brakes, handlebars, etc.
Id say if you already had a bike with disc brakes and you wanted to make an ebike out of it, youd end up spending 200 dollars on a hub motor, controller, throttle, and screen, and then 400 on a devent battery, which is a much cheaper build.
Sure, at that point you can get a motorbike, which is bound to burning gas, being loud as hecc, and stuck on the road. (and much more maintenance compared to a hub motor ebike)
Personally I dont do much pedalling, I basically did make an electric scooter, but its way more reliable than a scooter, has more torque, is stealthier, and I can take it more places.