When using the NGC
market values I tend to subtract around 20-30% from them, especially if yours are not graded and slabbed by them.
Also look at NumisMedia FMV @ http://www.coinprices.org/
I find their site to be fairly accurate on the classic coins. Pricing can be tough as almost any book will be out of date as to current price by the time it's published and hits the store. Online sold pricing is really the best example, but can still be problematic if you are pricing coins that are not generic and almost exactly the same as yours. So also take the online prices with a grain of salt knowing that fact.
"Buy the Book Before You Buy the Coin" - Aaron R. Feldman - "And read it" - Me 2013! ANA
Life Member #3288 in good standing since 1982, EAC Member #6202, NBS Member, 2¢ variety collector.
See my want page: http://goccf.com/t/140440