Eric,
The cost can be attributed to feedback. Not using feedback can be dangerous
to people or machinery. You can use digital or analogue feedback. Neither is
cheap. At the very least, you must use limit switches. Please also note that
steppers are very wasteful of energy and can slip when transporting loads
during acceleration and deceleration. Hydraulic, pnuematic and pulse driven
PM Motors are good choices, some require brakes, all require feedback.
Steve

"Eric Anderson" wrote in message
ps.com...
I have an application where I have to move a 3 lb object in a 3 ft
cubic space. I am not looking at high performance or high accuracy.
It can take as much as 30 seconds to traverse the 3 ft distance and
the accuracy could be no better than 0.020 or 0.050 inch (possibly the
spec could be even looser).

Linear actuators would appear to be the best solution, but I am
finding that they are hundreds or even thousands of dollars. The
product I want to build will have to cost no more than $2,000 for a 3
axis device with controller, overhead and profit.

What is it in a linear actuator that costs so much that you could not
build a low cost version using a threaded rod, servo or stepper motor
and an extruded frame for a lot less?

Does anyone know of a linear actuator that can provide the kind of
performance I am looking for for a couple hundred dollars?