01 S80 intermittent oil lamp
 

The oil lamp has been coming on (together with the "No Oil Pressure" message in the DIM), only during idle after running for a half hour or so. When it does this (usually at stop lights), I put the vehicle in neutral and give it gas until the oil lamp turns off. It never comes on above 1000 RPMs or so.

The oil and filter in this vehicle has been changed religiously for 12 years every 7500 miles using full synthetic.

What are likely explanations for this problem? What should I ask the mechanic to do? If this is a common problem, what is a typical estimate to repair (at 3rd party garages)?

first off, is there the correct amount of oil in the car
second, you can try to replace the oil pick up seals. that may fix it it may not. if that doesnt fix it, you can try the oil pump

Checked at idle, the correct amount shows on the dipstick.

However, after running the car for a bit, the oil bubbles up as in this image album: Volvo Oil Bubbling - Imgur

Is oil bubbling abnormal?