N+1

When you ride lots of miles like you do, the cost per hour is low.
25000 miles at 16 miles per hour average is 1560 hours. So a $2000 bike is only $1.28 per hour, and a $3000 bike is $1.90 (We'll ignore tires, chains, cogs, cables, energy bars, etc, since those get used up with or without a new bike)