7000 miles on a bike I spent 1800 on originally, then later added 400 wheels, a few sets of tires, a couple pairs of shoes, a couple pedal sets, chains, brake pads, shift cable, headlight replaced, cassette replaced... several kit sets... all told I'm about 3500 into the sport, so $0.50/mile.

Recently purchased a used hybrid for 500, added a used Tubus Cargo Evo, and about $60 in other parts, for a total of around 625 That one is quite new to me so fewer than 250 miles. So I'm still around $3/mile on it. That will improve as the snow clears out.

On the other hand I've lost 33 pounds this year riding about 2900 miles. Some of that has been commuting... around 200 miles of it, so that saved me 50 in gas and wear and tear on my car. But the health benefit if sustained will add a few years (all other things being equal) to my life, which will cost me more since I'll need groceries and housing for those additional years... But I'm happy to spend that money.