The oil pressure gauge drops to zero with engine running.
I can understand why you don’t want to pay to have it properly diagnosed, but that is false economy. Your engine may seize at the worst possible time and/or location.
Pay for the diagnosis, then decide which is right for you; repair , sell as a mechanics special with full disclosure of repair needed, or junk it.
I am not a mechanic but it seems to me the engine should have seized by now if this has been happening for very long. My guess is a failed sensor. Either way, have it looked at ASAP. Have it towed to the shop on principle.
If you get a mechanical oil pressure gage you can hook it where the oil sending unit is at. Monitor the pressure. If the pressure on the mechanical gage drops to zero or under 15 pounds, turn it off and tow it to a mechanic. If the mechanical gage reads good all the time replace the sending unit and check wiring.
That’s the way to do it if you already have a mechanical gauge. If you don’t, a new sending unit will propably be cheaper.
If oil pressure is good, it could be a failing stepper motor in the instrument cluster also. Is there an oil pressure idiot light also?
You probably have some oil pressure
What engine? How many miles? Does the engine have oil in it?
Does revving the engine increase oil pressure? Does the engine sound different when oil pressure drops?