Deceptive baggage charges cost more than the flight!!!

I bought a return ticket to Queenstown for about $260. On the way back to Sydney I did not check my baggage in online. When I arrived at the airport, I was advised that if I had to pay $320 (yes, that's right, $320!!!!) for my luggage, which is more than the cost of the ticket. I have made a complaint to Jetstar. All they have said is that I should have checked their website about what fees would apply. But hang on a minute - I didn't use their website at all to book my ticket. I booked it through Expedia, so why would I have any reason at all to visit their website? I was charged a fee that I was not properly informed about. It was a fee charged by stealth. Jetstar in their response to me pretty much admitted that since they are a low cost airline they have to gouge customers any way they can. Checking in online cost about $80. I could understand if I was charged $120 (a 50% premium), but $320!!!!!, that's simply a joke. For various reasons that day I was not able to check my baggage in online. I shouldn't be penalised with a fee that cost more than my plane ticket! This is a fee that was charged deceitfully to extract maximum profit from unsuspecting travelers. If Jetstar wants to not just advertise their services on Expedia, but actually use Expedia as the point at which the sale transaction takes place, they need to provide this information on Expedia, not just expect that every single passenger would visit their website to check what unexpected fees Jetstar might decide to throw at them. I am therefore asserting that this fee is unfair, unlawful and excessive. This caused an extremely bitter end to my New Zealand holiday, and I can not stop thinking about it!