guess that won't be cheap ...
but with a nice SDK it's worth a thought 
about if this stuff is overkill for a single pump : well, you could do it using operation amplifiers, but then you won't be able to log data, which is just a nice feature, and calibration wouldn't be easy. Those Atmel AVR controller basically need only one external resistor to pull up the reset pin, and then you just need to connect the inputs and outputs, assuming you already programmed that little thing. that's possible via a cable attached to 4 pins of the cpu and your parallel port. so it's quite easy. and that controller already contains normally 8 AD converter, quite some output/input ports depending on the package the controller comes in, some internal flash, eeprom and ram, different timers, serial bus, rs232 stuff ( though without level converter ), ...