How do you measure return on investment (ROI) for an electric bike? As we consider an e-bike vs. a car purchase, I'm trying to assess return on investment (ROI). My cost factors are, in order of priority, time, money, and carbon footprint. 

My commute


I travel 20 miles daily, 5 days/week, over moderately hilly terrain in a temperate zone with four-season weather.
I drive a ten-year old car that gets 45 mpg and has low annual maintenance costs.


Car costs


The car trip takes 20 minutes on avg., so time cost is 40 minutes/day, 178 hours/year, or 37 days in 5 years.
At a fuel cost of $2.30/gal, daily fuel cost is $1.02, or $267/year.
To buy another car like the one I own, according to Kelly Blue Book, I would pay $3,250. For sake of argument, I'll assume the car will last five more years.
Insurance costs are $552/year.
Maintenance costs include oil and filter changes and unexpected repairs. On average this has been about $800/year.
Cash outlay the first year is $4,869. Subsequent years would be $1,619. Estimated five-year financial cost is $11,345.
Estimated carbon footprint is 2,296 lbs of C02, or 11,480 lbs in 5 years.


E-bike costs


Testing e-bikes, trip time is ~40 mins. Daily packing prep time, a shower, and a clothes change add 25 mins. Normal time cost is 105 minutes/day or 467 hours/year.
Because of weather, I can't bike-commute daily. Of the 267 work days/year, I'll Uber on 30 of them. At 20 minutes per trip, Uber time is 20 hrs per year.
Adjusting for Uber, annual time cost is 435 hrs, or 90 days in 5 years.
With moderate motor assist, I consume approximately 300 Wh of electricity daily. Cost per kWh is $0.13, so fuel cost is $0.04/day or $10/year.
Speaking to local bike shops, the high side of annual maintenance costs is ~$150.
The e-bike I'm considering costs $3,000. Adding high quality waterproof panniers ($150), a pump ($20), tube ($5), seat post bag ($10), rain jacket ($100), lock ($50), and clothing ($300) brings the kit cost to $3,635. I will not add additional insurance.
Uber costs $22/trip, so 60 trips per year (30 days) is $1,320.
Adjusting for Uber days, cash outlay the first year is $5,115. Subsequent years would be $1,480. Estimated five-year financial cost is $11,035.
For the bike alone, estimated carbon footprint is 110 lbs of C02/year. Adjusting for Uber rides (265 lbs/yr), that translates to 363 lbs/yr, or 1,813 lbs for 5 years.


Over 5 years, the car is >2x better in terms of time. The e-bike + Uber mode breaks even with the car in terms of money. The e-bike + Uber mode produces less than 1/6th the CO2.

I'm not surprised about the time or carbon footprint, but I thought the finances would look more attractive. Where am I making incomplete or unsafe assumptions, and how should I modify these calculations?
It's only so expensive because you are going for the most expensive bicycle option on the market.  One could easily buy an $800 bicycle and spend $1000 on retrofitting a motor and battery and end up spending a lot less on the bike, or you could just ride the $800 bicycle without the motor, and save even more money.  You're spending as much on the bike as it cost you to buy a car, plus you are using Uber when not on the bike.  Most bicycle commuters will use public transit (bus or subway) when the weather doesn't permit riding. You aren't going to save much money when you spend $3500 on a bike and related accessories.