Don't be surprised if a mechanic replaces the switch with an aftermarket switch and you still have the problem. The guys here are speaking from experience. Especially since money is tight, your best chance of fixing it with one try is to replace the switch with an OEM one. We've seen hundreds of this problem posted here and on our own cars. It is pretty much always a bad switch. After many years on this forum, I don't recall once it being actual low oil pressure. If it ever was, I missed it. We've also seen many instances of the aftermarket switches not being calibrated properly (light comes on at idle) and replacing with OEM fixed it.
The light comes on when engine is at operating temperature, in gear, at idle? If you take it out of gear or speed the engine up, the light goes out?