The transmission fluid is supposed to be good for the life of the car, so that is a big flat lie that they HAVE to replace it at 30k miles. Check your service book for that information.

What you could (should) do is asked them to diagnose the transmission fluid: They take a sample of the fluid (or either put a probe at the place of the dipstick) and their computer tell them how is the fluid (it gives a number).
Depending if the number read is below the manufacturer limit, you don't need to change the fluid. If the number is close to or above, the "lifetime" fluid is shot and you need to change it (but that should not happen before you reach at least 100k miles). Ask them to tell you what the number is!!

I don't remember what the limit number is, and since your dealer is not trusthworthy, you should call Nissan corporate to get more information on that. With all this information, your dealer should stop think you are good to steal and be more straightforward with you.

As for the anti freeze, it is good practice to change it every two-three years (like the brake fluid) but not necessary.
Both fluids (anti freeze and brake) are not that expensive to change (you can DIY even if you want), that is the transmission fluid which is expensive (about 12$ a quart, I believe). BTW, for the transmission fluid, you absolutely need the nissan fluid, not any other one, so no independant mechanic for that, you need to go to the dealer.

At the end, with only changing the oil, oil filter, anti freeze and brake fluids, it should be about 200$ total instead of 600$.