One of my past rats did the same thing since she was a baby and she saw the vet regularly, who always told me nothing was wrong. When rats have URIs, you will likely hear clicking or chirping in their lungs when you put them up to your ear to listen. Their breathing may look labored if it's particularly severe and they may become sluggish. But if it's just sneezing (and maybe some porphyrin in the nose every morning) I'd say just keep an eye on it, mark any noticeable changes. Like I said, my rat lived 3 years and there wasn't a single day she didn't sneeze or snuffle a little, and she was active as ever and had a clean bill of health from the vet, so we concluded that it was allergies. I was always wary of changes and always kept an eye on how she sounded or how much she was sneezing; I think at this point, if they sound clear and are active, it would be practical for you to watch their day-to-day before taking them in and paying for more meds.
Whenever I took my rat to the vet for her sneezing, he honestly told me it didn't sound like a URI to him, but he would offer me antibiotics anyway if I was concerned about her. But because she had been doing that since I got her, wasn't sluggish, and had no noise in her lungs, I went home without the antibiotics and her condition never changed. If it was a URI it would have worsened within a few days, but the span of 3 years gave way to no difference. So I'd recommend you just monitor them. You see them every day and you know them well, so I'm sure you'll recognize it if something changes in their behavior & is not right.