I am doing the same thing you are. Fjestadt publishes books showing the expected values for guitars, guns, knives, and all sorts of other stuff. They have books for electric, or acoustic guitars. Many times your local library will have a book in stock, but it pays to check first and see when their book was published. Libraries can also borrow from other libraries just about anywhere in the nation, so if the book is at a library, they can likely find it without you having to pay for it.
I had problems finding value for a Martin OM-42 limited edition as it isn't in any of Fjestadt's books, but I got some help elsewhere.
The best suggestion I got for selling my guitar was to list it on Ebay with a reserve. That way, if my base price isn't met, I don't have to part with the instrument, and I don't have to worry about a guitar store lowballing me by 50%. Sure, I have to pay the ebay 20% commission, or $250 max, but that would be reasonable as the guitar I'm selling is worth quite a bit.
Guitar values vary based on locations. Some instruments are strong in one area, and weak in others. By putting your instrument on ebay, you get an international audience, and are thereby able to get away from some of the problems caused if interest in your instrument is weak in your area. You would get an idea of the true national/international value of your instrument.
I would try the local library first to look at the Fjestadt book for values on your guitars. Then, when you establish what the value is and what you want to sell it for, put it on Ebay with a reserve minimum amount.
Your alternative is to sell it to a guitar store, and they will treat you every bit as kindly as a local used car dealer would (I think you can gather my meaning there).