My vote would be for the CG, but I don't know if you can consider it quiet there because it's a prime fireworks viewing spot, but it's definitely romantic. AP and Jiko are a little more quiet... I think Jiko a little more so. And afterwards you can walk outside and use the night vision goggles to look out over the savannah and see the animals... I thought that was pretty cool!
I have to say that if they do choose the CG, it's not really oppressively expensive. We were on the Premium Package, so our meal was prepaid, but the totals on the receipts both times we ate there last week (the second night we cancelled an ADR somewhere else because we enjoyed it so much the first time) were reasonable for the amount of food we got. And if we weren't on the plan, we would never have ordered 2 apps, 2 entrees, and 2 desserts, so I think you could keep it pretty reasonable if you ordered 1 app, 1 dessert, and 2 entrees.