A pH or EC meter is only as good as its last calibration. Electrodes drift with use, and they degrade fast if the tip is allowed to dry out, so calibration fluid, storage solution and probe cleaner are running costs rather than accessories.
Here you will find pH 4.0 and pH 7.0 buffer solutions, conductivity standards including 2.76 EC, probe cleaning fluid and storage solution, from Bluelab, Growth Technology, Hy-Gen, Aqua Master and Nulife Technologies. Most items sit between $2 and $35.
A practical routine. Calibrate against both pH 4.0 and pH 7.0 rather than one point, since a single-point calibration hides slope error. Never store a probe dry or in plain water, which strips the reference junction; use storage solution. Clean the probe when readings get sluggish rather than waiting for them to get wrong. And do not re-use buffer that a probe has already been dipped in, because it is contaminated the moment it is used.