Please don't respond to me in this way. I am not a child. I understand that airlines can charge whatever they want. That is what happened. My complaint is: How does Frontier get away with stating they are a low cost airline when they are obvious not?
I agree with your final sentence. I think "low cost" carriers are a bit of a misnomer. Their base fares are usually cheaper but they squeeze you on the back end with all sorts of fees. These fees are usually optional (like seat assignments, charging for carry ons) but if you choose to not use these features your trip is likely to be more unpleasant. Usually when you add these fees back in their ticket prices aren't significantly different than a mainline carrier. What's just as bad is most of these budget carriers have no interline agreements and fewer flights which means when something goes wrong the passenger is often stuck. But people select them for the same reason you did - the initial price.
This is one of those times where I think having a good TA could have helped. They would have been able to present your best options and informed you of these fees that you incurred prior to your booking the ticket. Low cost carriers don't hide their fees but unless you go looking they're an unpleasant surprise which is what happened here.
I'm sorry that we can't do anything to advocate but I understand and sympathize with your position.