Classifieds on Ag Talk are free to use.

One note of caution do your own due diligence as far as contacts, accepted payments and such. Many using the Ag Talk classifieds have reported scammers claiming the ability to help them get in touch with willing buyers for a fee, and all the usual scams of buying for a family member in the military overseas, sending more than it's worth, and all the usual craigslist, shipping, check type scams.

Be cautious but trust but verify everything and everyone.

There are many good people using them and having great success.

Edit: Since you are not paying by the word a good description is very helpful along with many pictures of the actual item for sale and some sort of contact info. 

Many have posted they won't look twice at an ad without a picture or price price and dislike representative photos.

This comes from years of reading printed classifieds and seeing "call" or representative photos and finding out later it's not as advertised.