At first glance, yeah.. it does seem very expensive!
But... well, dolphin swim programs are expensive. That's just the general rule.
For example, here are the prices for similar or comprable programs at different facilities in Florida:
Dolphin Research Center (Grassy Key, FL) - $180
Theater of the Sea (Islamorada, FL) - $175
Marineland (St. Augustine, FL) - $179
Now, these are smaller and more remote parks (the first two are in the Keys, which are about 300 miles south of Orlando, St. Augustine is about 100 miles north). These don't include the other extras that Discovery Cove does (lunch & drinks provided, ray pool, coral reef, aviary, beach resort, etc). At Theater of the Sea, for example, they have a Ray Swim program which costs an additional $55. Or you could book a snorkel trip to a coral reef at $35-50 per person from a charter boat. But in general, you don't get all the extras that DC offers. Not to downplay their programs (I've done some of them and really enjoyed the experience!), but it's not in the same league as DC on the whole. Plus, it's darn expensive to drive down to the Keys and stay in an overpriced island motel.
By contrast, Discovery Cove is $289 (high season) / $269 (low season). It's $100 less if you skip the dolphins (which makes their actual dolphin program less than the other facilities in that regard). So, $189/$169 for the park itself.
When a typical adult admission ticket to a normal theme park (Sea World, Universal, Disney) runs about $65-$70 per park without food / lockers / towels / etc, it's not much of a stretch to imagine that an extra hundred bucks covers all the perks of DC.
Plus, Discovery Cove is limited attendance. 1000 people maximum. You're paying for the lack of crowds just as much as the unique experiences.
Yeah, it's pricey... but it's on par for the sort of experiences offered. Definitely a luxury destination, it's no surprise that not everyone can afford it! Heck, I love the place dearly and I haven't been able to afford a return trip since 2004 (but hopefully I'll make a trip this year!)
And hey... you get a free snorkel and a free group photo out of the deal, too.
=)