The "cost" of something is the price to be paid for it. "Costing" generally refers to the process by which one decides on what the cost is going to be [although in some contexts it can also mean the price paid, for example, "I bought two apples, each costing me 50 pence"].
Taking your two questions:
1. If the list includes details of how the price of each item has been calculated, it will be a "Costing List". If it is simply a list of prices, it will be a "Cost List".
2. Again, it depends on how much detail is included, but (assuming only one value is quoted) the correct usage is "estimated cost".