Possibly a bit out of the way but I have rented a couple of times from Sprockets Cycles in Redondo beach. They have a couple of different BMCs, it's expensive but you don't need a crazy deposit like you do at Helen's. They are also flexible on kitting them out, gearing was 53/39 with max 25t on the back which I asked them to change - they put a compact on for me. They have Red 10 speed kit.
Plus you'd get a nice ride home along the bay after you pick it up.
Did this route while I was out there. From Echo Park you can easily get into the Santa Monicas or even up Mt Baldy - would have loved to have tried that but too far from the South Bay for me