Is the cost ok? Availability pretty reasonable? Safe (enough) to ride throughout the city? Good locations? How far outside of Paris does the program extend to?
Yes, the costs are more than OK. You only have to pay a deposit. The bikes are great, and Paris is accustomed to cyclists (but I'm Dutch, so I was born on a bicycle).
The program is only inside Paris city. The locations are excellent; the only problem is that people don't want to drive uphil. In Montmartre it will be difficult to find a bike in the higher side. about 11 years ago