my car is getting old, and I don't want to spend too much money on it.
The "low oil pressure" warning comes on all the time, but I don't want
to fix that. So what if I contine to drive it with "low oil pressure"?

 

The vitals of your engine will not see the proper oil delivery/lubrication to keep them from breaking down, eventually.

 

bye bye motor (eventually)
(and it may be ugly when it goes)

 

KABOOM. get AAA your gonna need a tow

 

Spend a few bucks on a new sending unit, the old one may just be worn and the pressure could be OK. If not, a heavier grade oil can be a bandaid. Most cars have the light come on at really low pressure, around 4psi. Normally you would not want to see lower than around 15-20 at idle and 40+ at normal driving speed.

If the pressure is really that low, sooner or later a bearing will sieze. It could go years, it could go as I am typing this, hard to say.