There will never be an "economy of scale" here. For the motorcycle, if you need more battery, just slide it in. More power, just slide it in. Not enough room, just make it bigger. Not strong enough, add more iron.
The bike is a different critter. It needs to be a bike. Therefore you can't stick in a battery that makes yours legs split out at a 90 degree angle. You can buy a 10kw motor that weighs 40lbs for $200 bucks if you are building a motorcycle. The motorcycle weights 250-450lbs. Try peddling that sucker up a hill. Building a bicycle that'll run 30mph for 30mi takes a lot of work if it is still going to be a bike, and design of the bike, the micro motors, light weight and reliable drive systems, small controller systems, cost to engineer and build. A motorcycle could use a golf cart controller.
Economy of scale: Bought my GF an Ipad for Christmas last. Just bought a new desk top last month. My desk top has HD and ram with #s like the national debt. Gazzillions. Has a monitor as big as the tv and I almost have to push my chair back to see it all. Wonder of wonders, it cost $200 less than the f-ing Ipad.
Economy of scale won't work very well here, as you can't just throw bigger at a bike, and have it work. Micro costs $.