Ariel's because it's buffet? We're doing it there, and our menu is gonna be 95/person I think? The smaller Jiko wine room might be cheaper because there's no room to dance, but I'm not sure.
I tried to help anwser your questions in the box above. I would also recommend using a rehearsal menu for dinner to save money (I am doing this, and getting a ton of food for almost half price!!)