Discounted infant seat prices vary wildly among the various airlines. I've had the best luck with Southwest (60% off the regular adult fare, not ding), Delta sold me one at 50% of the regular adult fare. That's it, the other airlines don't really have a discount that I've found.
I had the same experience the OP did when I tried to buy tickets on American, double the internet fare I bought (from their website). Same for Continental, Northwest and United; I did tell the customer service person, nicely, that it sounds like the airline really doesn't care about infant safety since they don't offer a real discount on the fare. Every one agreed with me, it bothered them too but that is what corporate had set the price at; it's also the big reason I refuse to fly American Airlines anymore.
I haven't tried Jet Blue but they don't fly the cities I go to regularly, so don't know if they offer them.
I have always bought my dd a seat since she was 6 weeks old, the last time we flew and I held her, it was a miserable flight. She was cranky, I was cranky and the flight was CROWDED. I couldn't nurse her because we were packed in so tightly there wasn't room for me to get her into position without infringing on the other person's armrest; which he resented.
By the time she fell asleep I was dead on my feet as well; our flight had been delayed by a couple of hours. I couldn't sleep because I would "lose" my grip on her and she'd sag down in the Maya Wrap and wake up.
She is a great traveler and has logged more than 20 flights and she's just turned 2 years old. I have a sit and stroll carseat/stroller combo, works great for traveling; totally worth the money spent but it does get a lot of use. She's had her own seat since she was 6 weeks, is alway in a car seat and typically sleeps through most of each flight which typically range about 6 hours. I do book our flights around nap time or red eye to ensure she will get a good rest which means I get to rest and arrive ready to go.