OK, spent several hours reading about car audio. Yikes!! You can spend a lot of $$ very easily.
So it looks like I don't need to upgrade all 4 at once, or even upgrade the rears.
I'm with you David, $100 is about what I was looking to spend, but that will probably stretch... I don't listen loud, so I am hoping that I can stick with the existing head unit.
The only issue with the Hertz unit is depth. I think my front panel will only accommodate 2 5/16" deep speakers unless I carve up the door panel and install custom grills.
I might just pop in to a couple of dealers and play dumb to see what they recommend.