I was a C5 owner for several years, and I now have a C6 with RFs, so I can relate to this issue.
Quick answer to your question: yes there are quieter tires than the good year RFs and they are cheaper than RF tires... but there is also some trade off.
You will have to carry a tire plugging kit, jack, air pump, etc if you go with non-runflats. Even that did not save us when I tried the non-run flat experiment, because I broke one of the valve stems on the tire air pressure gizmo. (I ran it through a car wash...
) This required a tow, and it also almost cost me a motel bill.
One possible alternative is a different brand of run flats. I have heard that some of them are less noisy. Even the tires on my C6 (which are a different type of GY RFs) are quieter than the ones that were on my C5. I would look into that option before you jump to the non-runflats.
Good Luck though with however you choose to go.