: Is there a well known "blue book" type of thing like they have for the valuation of cars? I don't even know what to ask for in this department.

First of all: DON'T SELL YOUR BOOKS. You'll hate yourself for it.
OK - so your new location won't have as much space, it's hard to protect, pack, label & ship heavy boxes of books. Do it anyway.
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Now that I've gotten that out of my system....and you still want to sell your books......I actually suggest figuring out what you have.
I would suggest picking up a copy of
McBride POCKET GUIDE TO THE ID OF FIRST EDITIONS
or haunting your public library to help you figure out what you own.

Then figuring out what it is worth. Here is where many dealers START. Then they add knowledge of their market.
BOOK PRICES USED & RARE (Don't know author)
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Make a list, write down everything that appears on the copy right page, note if you have the dust jacket, if there are library (X-library) markings. On the copy right page look for the magic words "First Printing", a string of numbers 1 2 3 4 5 or dates 77 78 79 80 81. Look for strange numbers like H.10.66 and the copy right date. The numbers that start with LC or ISBN are the Library of Congress and International Binary codes.
Sometimes the LC number doesn't have the "LC" but have the YY-##### where the YY is the year.

Is the book signed? Has someone written in the book? Ex: "to Billy from Grandma" If a book is signed by the author this adds to the value. If it has a gift message, this is considered a minor flaw (except for major flaw in the book that my Mom impressed NUTS into when she was 10 - and it embossed 10 pages - good thing that my Mom doesn't have Web interface yet.) The exception to the rule this minor flaw is if you can prove that Billy was Prince William of England & Grandma is Queen Elizabeth - or similarly if Billy is the grandson of the author.

Make the list complete - neatness counts - and on the computer is best (later, if you are posting this information, you won't have to type it in again).

Now start to contact your book dealer friends - Don't have any? Well there are a couple who read this bulliten board - and also several names that are on Aethling's Andre Norton Web site (see Web Ring). If you are really selling your books, you might loose a little if you let someone buy most of them, but you will save yourself a lot of trouble. You might also get a dealer or appraiser to look at your collection.

All of these steps can come in any order. If you have someone that can come to your location & give you an appraisal that is again easiest for you.
Just remember that no matter what you decide to do, someone will still be packing up those books - I recommend that it be you and that the place that you are shipping them to is your new home.