pH Probe Costs

> Hate to ask this, but how expensive is expensive?  I've found several
> starting a $79.00 up to several hundred dollars.  Will the probe be
> run in line?  If so I have found one with a flat electrode that is
> designed to stay clean for I think $115.00.

Pet Warehouse or That Fish Place have a Boadley-James "Silver"
electrode listed for $33 or so.  We have three of these and they seem
to work fine - at least as well as the $90 electrodes they used to