A Norman Rockwell pricing guide titled "Norman Rockwell Collectibles Value Guide" can be purchased from either Amazon.com or eBay.com. Used copies are inexpensive, while new copies in good condition appear to be collectibles.
The Norman Rockwell Collectibles Value Guide, written by Mary Moline, has printed several editions. The latest edition (6th) was printed in 1988. The best way to determine the value of any Norman Rockwell collectibles is by comparing prices of your specific collectible and its condition with similar advertised pieces. Typically, it is best to get the collectible appraised by a professional.
Ebay has an information page surrounding Norman Rockwell collectibles, and online websites such as Worthpoint.com advertise the ability to appraise Norman Rockwell artwork, as well as many other antiques and collectibles.