I run a John Deere Dealership, and we use Actuators in many different situations on Ag/Construction Equipment-first one that comes to mind is the Fuel Pump shutoff (which is key actuated)-

The John Deere Part# is AM882277-

While it's not really cheap (about $200.00), it is a very heavy, Industrial type Solenoid-I worked for Case and IH, and, I can tell you that they were used on many different applications-if you are close to a Tractor Junkyard you might look there for a cheaper alternative-they are generally mounted on the back side of the Pump (so they aren't easily visible)-

Don't go looking at Equipment made after about 2002-they integrated them into the Pump around then-hope this helps-