A "hobby" grade linear motor
There are a number of kinds of linear motor. Which are you referring to?

Baldor makes a number of varieties, and their page has an excellent overview of the different types.

I'm most familiar with linear stepper motors, which are a type of linear motor. However, there are Brushless DC and even AC Induction varieties.

However, I will say that they are generally as or more expensive as a comparable stepper/servo motor and lead-screw arrangement, and are much less common on the surplus market.  

Given that, I think you would be better off trying to snag a long leadscrew on ebay, rather then find a similar sized linear motor. Then, just add end supports, a motor, and some linear bearings.

What are you trying to do, anyways?