Dwyer Magnehelic gauges are robust, work well, come in a wide range of
scales useful for piano and organ work and are relatively inexpensive
(the last one I bought was $35 new on Ebay).  Here's a randomly
selected link to a purveyor of a 0-40" range gauge (they do either
pressure or vacuum) :

   http://www.davis.com/catalog/product_view.asp?sku=6846272 

There are many suppliers and less expensive ones are often found (even
new) on Ebay.  We use them for many applications in the lab and they
perform well for many years.  They can be calibrated relative to a
manometer so you can be sure of accuracy over time.

Cheers,
Roger Wiegand
http://www.carouselorgan.com/