What about something like the 23L2 motor from this page:
http://www.anaheimautomation.com/pro...75&pt=t&cID=19
connected to a leadscrew setup, driven by this driver chip:
http://www.sparkfun.com/products/10735
Assuming the stepping + leadscrew combination could create fast enough motion with enough torque/thrust, it seems to put the price point in the right ballpark.