Well having ridden the Paris Velibs the idea is that most rides are intended to be free (ie you pick up a bike, ride across town and drop it in at another station) - takes less than 30 mins.

You pay a deposit to use the system at all - well it was some weird Credit Card thing for me. that was refunded at the end of the day. which deters theft.

The ongoing maintenance and upkeep of the bicycles is funded through the advertisers on the stations (i think, or that may be in Barcelona). the local public pay a nominal fee of about 20 Euro a year to use the bikes.

It was really handy in Paris. but it does have some problems - the bikes continually need to be redistributed as they collect in bunches 'downhill'.