For a few years i was a sound quality judge for IASCA (mid to late 1990s, sometimes partnered with tech ed of CAE/CSR Bill Burton) and years before that helped with custom car audio installs (late 80s to early 90s in FL). Yes, you can get very impressive car audio sound for 'reasonable' money. Great suggestion would sound isolation (read Dynamat the door panels, etc) first. Reduce the floor level noise, THEN add in quality drivers and amplification/source unit. Of course speaker POSITIONING and system tuning are key, so seek a talented installer with a good set of ears.
Cost? A few grand to far, far more.
As for the Bentley, the sound was good yet there is far better out there (judging sound quality, not the car). Have not tried the Pana yet. i use standard IASCA parameters and disc to judge the Bentley.