Hello bookjunky, Welcome to the forum
I ride everyday to work round trip about 14miles. I've been using the same motor for five years and 4,000miles.
For fun I can put anywhere from 30-70miles on a trip. I also made a 140 mile trip on my little two-stroke.
These motors can be very reliable with the right care and maintenance.
The two strokes take a lot of maintenance and tinkering to keep them running but once you get the bug's worked out they are a blast.
You could also look into a four-stroke which has a lot less maintenance but the cost goes up. I have heard nothing but good things from the Titan that Dax sell's.
If reliability and maintenance is something that you are really worried about you might want to look into the Titan.......bicycle engine kit, bike engine, bicycle engine, bicycle motor