You must have been on my site looking at the Betta Flo's and the Hydroflo. The Hydroflo is a 3" pump. That's the reason for the large price. And the Hydroflo is not a 30 gpm pump. It's 12 gpm pump. You don't want that one for what your doing.
How deep is this 20+" well and what is the water level?
The two wire pump is just fine, you won't need a three wire motor with the control box.
Either steel or PVC is ok. If you have acidic water, I would use the PVC. Don't worry about the pump flopping around in the well, it won't. A slight twist when it starts and that's all that is going to happen.