ServoCity, the guys who make those awesome servo gearboxes and pan-tilt tables have a new product, 12V feedback linear actuators:
For a hundred bucks a pop, and a variety of stroke lengths, you get 115 lbs of force at 0.5"/sec, with a 10K position feedback potentiometer and built-in limit switches. That’s a bit on the slow side (trade-off for the high force), but half the price of comparable, open loop actuators.
For twice the price, half the speed, and half the force, you can also get one of their new 4.8-6V hobby-servo-protocol linear actuators.
They too come in a variety of sizes/stroke lengths, and while they are quite pricey ($200), it’s a great deal for a linear actuator that can be powered and controlled just like a standard hobby servo!
They also have a tantalizing coming soon graphic for a smaller light duty version. Maybe it will have a lighter price tag as well.