Commuter checks on sale with $30 each (face value $35, =15%off);
if you would like to buy 5 checks at a time, commuter checks on safe for only $140 (face value $175 in total, =20% off).

Currently I have 14 checks for sale, and cash only.

Commuter checks can be used for VTA, Caltrain, Bart, SF Bay Ferry, and even at a couple parking garages at SF city. There would be no expiration after you deposited the money into clipper card (which can be applied at any Walgreens nearby, $3 each card). For more details about the usage of clipper card, you can find them at: https://www.clippercard.com/ClipperWeb/