It depends on where you shop. I can probably beat these below btw:http://www.allelectronics.com/make-a-store/item/SOL-132/SOLENOID-VALVE/1.html
12 Vdc, 100mA solenoid valve. Open when activated. Body: 24mm diameter x 31mm long. 62mm overall length, including inlet and outlet ports and terminals. 0.19" diameter ports. Used, removed from equipment.
Analog servo motor. Standard size, 1.55" x 0.73" x 1.46" (39.4 x 18.5 x 37.1mm). 49oz-in torque @ 6Vdc. Speed: 0.23sec/60 Degrees @ 4.8V, 0.19 sec/ 60 Degrees @ 6V. 6.5" leads with standard 3-conductor female connector.
Ledex(TM). 0.5" diameter x 1" long tubular solenoid with 3/8" diameter threaded bushing for mounting. 1/16" diameter x 1/2" long plunger. 40 Ohm coil. Operates on 12 Vdc. 1" wire leads.
$2.75 ea --- some caveats, provide your own return action and armature hold
A customer from CA US
armature not attached
I haven't used these in an application yet, but it should be noted that the armature (the actuating pin of the solenoid) is not retained within the solenoid body. In other words, if there is no power to the device, the pin can fall out the back. If you plan to mount the solenoid vertically (with the pointy end facing upwards), you will need to have something behind the solenoid to keep the armature from falling out.
A customer from Midwest USA
Wimpy little solenoid
Very limited push power. Maybe 1/8 inch of stroke is usable for any kind of push. Will push very lightly on 2 D batts, stronger on a 9 volt batt and a bit more on a 12v SLA. Still wimply and no way to hold in the piston from falling out.
A customer from Canada
can anyone tell me if you can remove the body or outer shell from this solenoid? all i need is the coil inside.
A customer from Near Sacramento, CA
Doesn't have spring return
The solenoid does not have a spring to return it to a retracted position when power to the solenoid is cut. Like the other reviewer mentioned, it does not have a back to keep the pin in when turned upside down (so that the pin pushes up when power is applied). I mounted the solenoid upside down (making sure the rod didn't fall out the back) and the solenoid would not always retract with the force of gravity after I triggered it. I was able to drive it with 5V and 9V and it has nice holding force.