It depends on how quiet you need.
The luxury brands with heavy suspensions are the quietest. You'd be looking at an older car or high mileage in that price range. Also, repair costs are high for luxury cars. And the mpg's stink.
But there's a vast, noticeable difference in loudness when you jump down to the lighter-weight cars and SUVs, notably in road noise and when hitting bumps.
Each weight category has its own noise level.
You'll get the picture really quickly if you test drive a few heavy luxury cars (in which you can whisper) and then hop into some lighter-weight cars (which will loosen your teeth).
Car salespeople often don't have the same perception of quiet as you, so you can save lots of time by asking the salesperson to show you cars by weight category.
If you're coming from a sports car, though, many cars may seem quieter to you. If so, you'll have lots of choices.