I've never applied because I know we wouldn't qualify financially. I'd definitely suggest calling the CF Legal Hotline. Beth Suffian (see the CFF.org website) can tell you if your situation is worth pursuing harder.
You might consider buying a hospital indemnity plan through an insurance carrier. They are relatively inexpenisive (under $200 over the course of a year) and it will give you a set number of dollars (depending on the plan but lets say $50 for example) each day your child is hospitalized. This is NOT for medical insurance, it covers the things your insurance doesn't such as missed days of work, parking costs, meals at the hospital, etc.
To buy one with an already diagnosed CF patient is going to be a bit more money and it may have a waiting clause before you can collect (so if he/she goes into the hospital int he first year of the plan it doesn't pay out, but thereafter it does).