1. 1EA Arduino microController - I love the outdated Duemilinove, but you can use just about ANY of the available models for this rather simple project. I bought mine from www.SparkFun.com for approximately $34.
2. 2EA DesignFlex PSF102 Series Pressure/Vacuum Switches, Part Number: 7882-710. Visit their web site for details: www.designflexswitches.com/switches/psf102.php. I purchased my switches through www.Globalepower.com ((847) 965-9808) for about $18 each.
3. Several Feet 1/16" ID X 3/16" OD Tygon Tubing, available from McMaster-Carr (www.McMaster.com) under their Part Number: 5466K31, for $1.09 per foot.
4. 4EA 1/16" X 10-32 Barbed Tube Fittings, available from McMaster-Carr under their Part Number: 2974K123, for $4.21 per package of 10.
5. 1EA 3/8" X 2-1/4" Polycarbonate Rod, or equivalent, for the Mouthpiece. Look at McMaster-Carr's Part Number 8571K13 at $1.82 per foot.
6. 1EA .65" X .50" X .25" Polycarbonate/Acrylic/Plastic/Delrin/Brass (your choice) small block to make the "Y" Manifold from. Even Easier - Purchase this part from McMaster-Carr with their Part Number: 2974K391, but you'll buy a package of 10 for $7.10.