How 'bout a DC driven diapraghm pump? I know some old Epson printers (The Stylus Color 660 for sure) actually has an all plastic diapraghm pump to remove excess ink from around the printheads...they can be picked up @ the local thrift store for less than $5(US) and also have a couple high power stepper motors and some other parts...
The only hard part would be removing all of the old ink.
(kinda off topic - back on now)
For a mini air compressor, why not use PVC and a geared motor? It could run off of two one-way valves (one intake, one output) and pump as much PSI as the motor (and PVC) can handle. I'm planning on making one for various applications myself.