for EC: Why don't you just use stainless electrodes sitting in a small reservoir with a hole in the bottom. A $2 pump could fill this every 5 or 10 minutes (depending on how often you wanted to measure), the measurement could be made and the fluid would then drain away.
for pH: what about the principle of a lemon battery - this uses different electrodes (typically a galvanised (=zinc) nail and a penny(=copper)) to chemically generate a voltage from acidity in fruit. I would have thought this should work for any liquid solution enabling an arduino to measure the voltage for a cheap pH meter. (Obviously you would have to measure the EC first with identical electrodes then correct for changes in the ions in the solution).
$170 for the above probe seems cheap for a large scale commercial project, but ridiculous for any sort of home/school project.