How much does it cost to treat a URI in a rat?

One of my lovely ladies had a bout of sneezes earlier and her breathing sounded a bit funny... Sort of like a kid with a booger in his nose lol! Anyways, I'm guessing it's either a URI or allergies. I use carefresh ultra bedding but the tree pollen in my area is excessively high right now. I actually just had to go to the doctor and get perscription nasal spray and allergy pills for the first time ever... He said most of his patients had come in for the same reason. I don't keep the window open in my bedroom (the room they're kept in) but there are a few open windows throughout the house to keep it cool (since I live in southern California). Is there a possibility it's just allergies to the pollen in the area? Or does this sound more like a uri? Is there anything I can do at home to cure her allergies? I wanted to see if there were any at-home allergy-fixers before I make a vet appointment. Also, if it is in fact a uri, how much do they cost to treat?