Hi mlesnick,
In addition to your budget … it would also depend on what you mean by organic. There are many uses for the term ranging from more of a marketing description that is somewhat interchangeable with “natural” to mattresses use materials that have an actual organic certification. In some cases there is little difference between natural and organic materials of te same type (such as in the case of latex) and in some cases there are non certified materials that can be more “pure” and use better farming methods than the same materials that have a certification (such as some types of wool).
There is a little more about organic certifications in post #2 here and post #6 here has more information about the different types of latex including organic latex.
There is also more information and links in post #2 here about natural, safe, green, and organic materials that can help each person answer the very complex question of “how safe is safe enough for me?”.
This is such a broad and wide and wide ranging topic that it would probably help if you had more specific questions or had a better idea of the type of organic materials you were most interested in.
Phoenix