Production cost typically vary depending on how much they are able to produce and sell and what you mean by "production costs". The fixed capital costs such as facilities and machines tend to make up most of the initial investment cost of production. Then during production there is the cost of labour. There is also research and quality control testing that is done to develop new products and maintain standards with old ones. For fixed costs, research, and labour, with greater volume of production and sales the production costs are lower per unit.
The actual contents (cocoa, wafers, caramel, sugar, vanilla and other flavours, wrappers, boxes) are relatively small compared to labour. Then there is distribution, and marketing costs as well as the mark up by each retailer to cover their costs and profit. All of which contributes to the final retail price. If you find a publically traded chocolate company, get their annual report and they should out line each of the costs (e.g., fixed capital, labour, supplies etc.).
Oh, if you wonder how I know this, most its from watching too many episodes of "Hows it made" and similar educational shows on TV, and a tour of a chocolate factory in Niagara on the Lake -- my youngest son was fascinated by factory production.