I also have a very cheap pH-meter (12 Eur or so) and was concerned that it wouldn't work for long. The electrodes are very sensitive for drying out and after not using it for some months the readings were wrong. I let it stand in a glass of tap water and after about 15 minutes the readings were reasonable again. Surely not the "official" method and not scientific in any way, but for me it works. I use it now for about 2 years.