It's a Sierra APH6-B or C. If the earcups are covered in leather, it's a B. If they are covered in plastic, it's a C. The B version is the one used to create the Rebel and Imperial flight helmets for ANH. However, the only differences between B and C are the material used to cover the earcups and the type of foam used in the liner. They are identical in outer appearance.
I got mine for $140 including shipping on eBay. It was in reasonably good condition, but all of the electronics were stripped out. Perfect for prop conversion perposes. Complete helmets in good condition with all of the electroincs in place go for around $300. If you have the complete mask and air hose along with a complete helmet: you are looking at $500-$600.
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