Here is Randy's site that will give you an idea of prices...
http://freeminds.org/sales/booksale.htm
http://freeminds.org/sales/booklets.htm
Here are some Ebay prices...There used to be much more listed, but it is getting so hard to find, and prices continue to climb.
http://search-completed.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&catref=C6&from=R32&guest=1&satitle=jehovah%27s&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=75211&sabfmts=1&fis=2&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=3%26fsoo%3D2&fgtp =
http://search-completed.ebay.com/search/search.dll?sofocus=bs&sbrftog=1&catref=C6&from=R32&guest=1&satitle=watchtower&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=75211&sabfmts=1&fis=2&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=3%26fsoo%3D2
Study this for a couple of weeks, and you will see some rare books come up. Photo Drama usually goes for $100-200, Daily Heavenly Manna goes for $80 and up depending on condition, Studies in the Scriptures, Millenial Dawn, etc. go for good money with the first printings worth the most. A complete set of the very first of bound volumes in a set of 6 average $1500, with single volumes going for $200-250 each volume. Unusual things, such as postcards, pictures, convention programs, banners, etc. are VERY Collectible and usually start bidding wars on some of the rarer stuff. Keep on the lookout for a book called Three Worlds. It is the rarest book of all, and only a handful have been found, and they are worth a minimum of $4000 and up.
If you don't have the time or energy to list everything on Ebay, there are Ebay drop sites in Cities that will list things for you, and arrange all shipping, etc. and will keep a percentage (anywhere from 25-40%) on average, and you get the rest. And some times the percentage drops if you have a lot of things for them to list. Not bad for not having to do any work, it is all done for you. And, they can't really cheat you, because you can see your stuff on Ebay and see exactly what it sells for.
Good luck!