I lock my commuter up at south hayward BART (got a bike locker). I take it homes on some weekends. I'm amazed that hayward BART has no lockers left. When I got my locker at south hayward they had at least 12 left. If south hayward isn't to far out of the way you might think about it. I did south hayward because there is a bike route to where I'm going.

I was $55 for a year for the locker ($35 for the locker and $20 for the deposit on the key).