Wow. Yes, that's a very good price, assuming they're in decent shape.
On your tractor, the power band will probably be between 2000-2800rpm. Does your tach have any markings to indicate what your PTO rated rpm is? (Mine is 2580) Try operating in the 2200 2600 range. Just see what sounds and feels right. You really don't gain anything by running faster than the PTO rated rpm. In fact, most implements don't like to be run faster than 540.
Look for PTO rpm markings on the tach.