Magnehelic model 2030 has a range of 30" water gage.  It can read either
vacuum, pressure or differential depending on how you use the ports.
It is about 4" in diameter and accurate to 2%.  The cost is low.  Screw
a rubber tubing nipple with a 1/8" NPT pipe thread on one end to the
low pressure port and it's a vacuum gauge.  Put it on the high pressure
port and it's a pressure gauge.  Click on the catalog page:

  http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=26 
  Series 2000 Magnehelic Differential Pressure Gage

Note that they offer a plastic box and all the stuff you need to make
it into a portable gauge complete with rubber tubing: part no. A-432
shown in the catalog.

I carried one of these in my briefcase without the plastic box for ten
years on several hundred plane rides and it was never damaged.  It got
to be scratched badly, but it always worked.

Don Shenbarger