I'm a little familiar with PH testing for aquariums (usually strips or vials) and soil for planting (vials or sensors). What's nice is that these tools are generally very easy to find and pretty affordable (there are lots of PH measuring tools marketed to home or hobby users, so depending on whatever else you might want to be testing along with the PH there may even be an all-in-one tool available.
I also recently came across some DIY methods, using vinegar or baking powder to test for acidity or alkaline reactions (divide into two containers, make a sludge, see what provokes a reaction)... there's even a test that relies on observed color change in water colored with red cabbage leaves. Would be interested to set some of these tests up to compare to one another!
I was on Amazon and found a bunch of pH meters under $20. Supposedly good from 0-14 pH, but that is very unlikely. Still, for the cost, it would be worth considering. Resolution was only 0.1 , but still, not bad.
PH paper can have interferences. Oxidizers like bleach can mess them up. It doesn't take much (ppm). This should be rare but can happen around, say, industrial sites.
PH meters, around pH 5.5-7.5, can get drifty. This usually happens with pure water and is cured by adding small amounts of KCl. Above pH 11.5, don't trust a ph meter unless it's specially made for that range ( alkaline metal error).
Recalibrating is another issue, when and if needed.