You should be able to get several applications out of a 30mL bottle... I have never used the "regular" CQuartz, but I have used CQuartz Finest, 22ple VX1 Pro and Opti-Coat 2.0.
I just did a Toyota Avalon this weekend with 22ple VX1 Pro and I used about 6-8cc's, and that is a LARGE sedan. I tend to spread it on quite thick, too.
From this, you should expect to get multiple applications out of a single bottle if done properly. The applicator makes a big difference as well.. I love the CQuartz Applicator Blocks wrapped in the suede microfiber. They soak up almost no product, so you are spreading it all on the surface instead of loosing it in one of those yellow foam pads.
*I have heard CQ original is somewhat difficult to work with compared to many of the other coatings on the market. CQ Finest and 22ple VX1 Pro are by far the easiest coatings I have ever used... why not look into the 22ple lineup?