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Riding a bike to work was the best thing I ever did for myself. My commute is 9 miles round trip and mostly flat, though. 18 miles is within reason, but would be pretty tough the first month. Your body adapts quickly. I do 50 mile rides for fun on the weekends now. I think an e-bike would be great for you, OP. I don't think a scooter makes sense for that kind of distance.
I have an expensive high-end 80s road bike I restored, a modern steel fixie, a 90s mtb I restored and turned into an upright commuter, and a few euro 3-speeds, but the one I end up riding most often is the piece of shit 80s beach cruiser I bought for $10. I just wanted to take the fenders and rear basket off it and throw it the frame away, but I ended up klunkerizing it with some parts I had laying around. I wouldn't go spending a lot of money on a bike, especially if you're trying to save up for a car.