Why go to all the hassle and expense of getting a prescription when it is specifically allowed by TSA? Worst case they confiscate it (unlikely) and you are out a $5 bottle of saline. Or if really worried about it, head to Walmart or Target and pick up a few 99 cent 2 ounce bottles of Renu (cheapest I have found). If it is not your brand, dump it down the drain and refill the bottle with your preferred solution, and into your baggie they go.