Well some of those NR4s are pretty rare. So ya got to know what you are looking at. Does it have the warning on the barrel, does the cyl. have the firing pin grove. Knowing the serial number would help.
I gave around $400 for a new in the box with shipper NR4 S/N 65-25220 about 3 years ago The RENE states the S/N range 64-16570 to 64-24942 and 65-06246 to 65-94966 The NR4 is the scarcest and the NR9 the next scarcest.