I rode on Frontier a few days ago. Checked a bag and carried one aboard. Ninety bucks at the counter, for the bags. They wouldn't serve a cup of water without paying. I overheard the flight attendant tell a passenger, who asked for a drink of water, "We sell water. We don't give it away. If we did that, every passenger would fill their bottles and backpacks." I was disgusted.
That said, given your options and offers, Frontier. Just hydrate before you go and don't carry anything bigger than a paperback. Or sit in thin, very uncomfortable seats for six hours. And pony up forty bucks to sit by a window. Or aisle. Or eighty or a hundred for the exit...