I'm also thinking about getting a standing desk soon. I'm inclined towards something a bit fancy that has a crank to move the entire surface up and down. I have a lot of equipment (monitors, desktop equipment, gaming equipment, laptops etc) so I want as much space as possible to be raised. Also, I want it to be easy to convert between sitting, standing, and treadmill mode.
Unfortunately this setup is looking expensive - $300-$600 for the desk and $50-800 for the treadmill depending on whether I rig a treadmill designed for running or get one specifically made for desks. At the same time, I can spend up to 12 hours a day at my desk, so it doesn't sound totally crazy.