You can always do it manually, mounting the camera on a rail. Not as accurate as neuro's suggestion obviously, but good enough for a lot of situations.
Indeed - I still have to try this one, but did read about it on the web.
The setup consisted of an X and Y rails, along with a rotating head. Then one have to locate the lens nodal point, and attach a string aroung with a small weigth in the leftover string - it should almost reach the ground.
Once established the center point of the whole panno, the guy was using the corresponding ground point to position the camera and lens, while keeping that string vertical with the ground reference point.
I am not describing the whole setup, but just giving an idea of from the pictures and notes - the webpage did a way better job
So, it's possible to do it without spending over 600 bucks....butyou have to work a bit more