Adding Values Of Checkboxes?

I'm currently designing a website for a takeaway company, and have one page displaying their menu. So that customers can easily calculate how much their takeaway will cost, I'm going to put checkboxes next to each item.Each of the checkboxes' value will be the price of the item, and I need a script that will add the values (prices) of the checkboxes they've ticked.They can then see the total cost of their takeaway without having to work it out, and add or remove items accordingly. I will then add a button which will print out a list of the items they ticked with the total price at the bottom. The customer can bring this in with them and the staff can easily see what they want and how much to charge them.

Firstly, I need to know how to make Javascript add these values (and probably save them as a variable) Secondly, how would I make this display on the page (either after they click a button, or automatically so they can see the price real-time)? - I assume this would be basic coding --- document.write(var) And finally, how could I make a script which would print only the items which are ticked, and the total price?