Oil pressure light questions

I have a 97 Cavalier that I bought in October. It had 79 K then and now has 83K. I went on a trip to the Panhandle in January. I had no problems with the car. It has lots of pep and drove straight through with only one brief stop. On the way back, when I stopped to get something to eat, I noticed the oil pressure light go on. I put it in neutral, gave it a little gas, and then it went off. I checked the oil and saw it was down a little, maybe a half quart. I topped it off. And the light did not go back on.

Then last week after driving about 70 miles, partially in a traffic jam during which I was bumper to bumper for over 5 miles, just crawling, when I got off the highway, the oil pressure light went on when I came to a stop light. Again, the same thing happened: gave it a little gas and it went off. I checked the oil; it was down about a half quart – I had gotten an oil change a little over 1,000 miles from that point. The light did not go on so long as I was in motion, and on my way back home did not go on. I topped off my oil. The light has not gone on since.

My suspicion is I need an oil pump. I have priced it as a couple of places and they are telling me between $400-$600 for labor and parts. Some people say it could be the sending unit, but does this make sense if the oil pressure light only does at the times I’ve described? Any suggestions about what to do with the car? I have spent a lot on fixing it and don’t want to look for another, for at least another year.

The guy who sold it to me, by the way, wasn't honest, and though I did a vin check, which checked out, I think he may have or someone may have rolled back the odometer.