I bought a 2 pH meters several months back from Amazon for roughly $10 a piece. I couldn't tell you how they work, but here's the link on Amazon: http://www.amazon.com/gp/product/B0087LOWIA/ref=wms_ohs_product?ie=UTF8&psc=1
I also got a neutral buffer solution for calibration. It worked fine initially but I'm thinking it's off. It's now being used for pH testing in the salt water of an floatation tank (147 gallons of water + 750 lbs pharmaceutical grade epsom salts and 50 pounds of dead sea salt). One meter shows a pH of 6 and another of the same kind at about 8.
My question is, does the salt effect the accuracy of the meter? Are the meters inherently bad, or do they need periodic recalibration? I didn't want to keep buying litmus paper.