As rkkwan says, people at the ticket office will encourage you to buy tickets at the ticket offices at the foot of the steps, but these are not required if you simply want to go up the steps and walk around the platforms at the base of the Buddha. The exhibition is, frankly, not really worth paying money for. If you decide you want to eat some vegetarian food at the restaurant then there is an area where you can do so in a normal cafeteria style just paying for what you want. The ticket sold at the base of the Buddha includes a sort of set meal at a fixed time in a "school lunch" style - I would suggest just the pay as you go option.