In a pinch, you could get by with a keyboard sustain pedal (KB1 > TIP for switching between intervals), and the Active / Bypass on the PitchFactor. It's fairly easy to build a 3-way aux switch with an enclosure, three momentary switches, and a couple of diodes. There are schematics and YouTube videos around the 'net. You're right: a lot of commercial switch sets are expensive for what's actually in them.
At some point, I found two Boss FS-6 dual footswitches on sale for less than a single DigiTech 3-way. I like the heavy-duty switches (same as the FCB-1010 or Roland MIDI pedalboards). They also have momentary/latching switching, polarity switching, the ability to gang several together, or use the aux switches individually. The downside is that they require 9V to work and power the LED's.
The bottom line is that you can make aux switching work with any one, two, or three momentary switches; even cheap-o Radio Shack switches. Holding up to the abuse is where the more expensive options figure in.
