This saving in electricity, or what ever form of energy you are purchasing will more than pay for the seal in less than two years. Use only the balanced type with low friction faces. Be sure to set the face load properly and remember this has to be done when the pump is at its' operating temperature. A cartridge or split seal is the only way to set face load. Those designs that adjust to the back plate are the exception.
Open impellers have to be adjusted to keep the pump running efficiently.
The seal must be repositioned each time the impeller is moved. Again, cartridge or split seals are your only option. Be sure to vent vertical stuffing boxes to prevent air from being trapped in the stuffing box. Good seals have this vent located in the seal gland. Make sure dual seals have the barrier fluid circulating either by convection, a pumping ring, or through a forced circulating system.