All depends on how much money you have in the budget.
I just dug out my old Extech DO meter that's been in moth balls for many, many years. A little PM on it, clean the electrode, replace membrane, new KCL solution, calibrate. Works like new.
You can get multi-parameter meters, but they could set you back quite a bit.
I have to dig out my PH meter. I know it needs a new bulb, but might be cheaper buying a new one. Those don't last that long.
