I've been looking through a 1971 NEC I acquired a while ago.
The prices listed inside the front cover sure contrast with some of the current amounts I've seen mentioned on ECN.
The following schedule of prices applies for single and multiple copies of this edition of the 1971 National Electrical Code:
1 to 4 copies: $3.50 each
5 copies or over: $3.25 each
And so on down to $2.30 each for 500 or more!
Oh and if you want to get really fancy...
An attractive hard-cover edition (NFPA No. 70HC) is available for $4.95 per copy.
Prices quoted are F.O.B. Boston, Mass., Taxes not included.