Mana Mushrooms

An overview section from within a resource I use.

TMGN

Information on everything from price to sales to production broken out along various axes in spreadsheets.

USDA Data

I don't know about the crystal ball title, but the trend information is good enough for the financial services industry ;-)

Trends in Mushroom Cultivation in the US

Mushroom Expert

A great resource and major contributor to the field:

Specialty Mushrooms by Daniel J Royse

This document includes production methodologies for various species.