Assistance with IT coursework

I am a beginner in excel and am doing my GCSE coursework.
For this, I am making a smoothie calculator. Basically the idea is the customer says 'I want an apple and banana and err orange smoothie' and then the shopkeeper figures out the price using this calculator. So on my calculator I have the names of the fruits in one column , and in the cell next to the fruit name I have a a dropdown thing. what I want to do is to have a list of the prices of each fruit somewhere else invisible on the page, and the shop keeper use's the drop down list to select, say, 2 oranges. So the number 2 will appear in the cell next to the cell saying orange. It (excel) automatically calculates the price of 2 oranges and adds to a different cell at the bottom, where the whole smoothie price is calculated. This cell will also have to automatically add on the price of ice and any other fruits that have been added by the shop keeper.
How do I this? can I do this on excel? Tell me if I need to explain more
also once this is done I have another question

Also after reading the rules I have realised I've cross-posted. However it is not on a excel help forum nor one based on computers and I have posted basically the exact same thing so I do not see the reason to post the URL?
no-one has replied anyway and are not as expert as you guys. any help appreciated