I would think an X-ray would show a hairball that is too big to pass, so pursuing asthma or an allergy, and the URI PCR is worthwhile for your kitty....in the meantime, you might consider what sort of household cleaners you use; even perfumes or essential oils can cause asthma or allergies in animals. Cigarette smoke, candles, plug-in air fresheners...these are all notorious for causing allergies as well as dust or pollen.
Here's a link to the only vet college in Florida. It's in Ocala, a short drive from you.
http://www.vetmed.ufl.edu/
Keep us posted on what you find out......