Compressed Air Best Practices, Mar. 2017, by Don van Ormer.
http://www.airbestpractices.com/industries/plastics/plastic-extruder-reduces-compressed-air-use-367-cfm

"A plastic product manufacturer spends an estimated $245,000 annually on electricity to operate the air compressors in a compressed air system at its plant located in a midwestern U.S. state.  The main manufacturing process is plastic extruding. The current average electric rate, at this plant, is 7 cents per kWh. The compressed air system operates 8,760 hours per year and the load profile of this system is relatively stable during all shifts."