The second edition of The New Wigmore Treatise on Evidence: Expert Evidence by David H. Kaye, David E. Bernstein, and Jennifer L. Mnookin, now will be sold in paperback. Previously, Aspen Publishers only advertised this work as part of the $1,195.00 five-volume treatise spanning many topics in the American law of evidence. This new edition (2011) contains additional chapters on forensic science evidence, and the majority of the book deals specifically with scientific evidence. At $240, it is still too expensive, but it is highly recommended.
Disclaimer: This recommendation, coming from the lead author, does not mean much.