Milwaukee Instruments pH600AQ ~$21
Calibrates well, has a screw for adjustment on the back, needs storage solution, needs break in time. I've had mine over a year and it's always been darn close if not consistently spot on in cal fluids. The first month or two it drifted a bit. Once a week calibration needed until it settles down.
EDIT: It's not as fancy as blue labs or apera. It also needs a bit longer to read steady. So let it sit for a minute. Other than that I've been very happy.
The Milwaukee Instruments compact pH pen tester is often used to help maintain pools and aquariums as well as improve results for growers and quality in a range of food and beverage uses.
milwaukeeinstruments.com