Have you done any research on whether there is demand or not in the market for your product?

Product costing will consist of the following
1) mould cost
2) material cost
3) production cost (power, water, labour, etc)
4) packaging cost
5) etc

mould cost
1) complexity & size of product
2) material of product
3) annual volume
4) shelf life expectancy of mould
5) etc

material cost
1) type of material / materials
2) production cost (if mixing is required)
3) etc

do you have injection moulding machine to run your product in?
is there any certification required for your product? to get certified, there's another cost to it.

it's not merely make and sell, do a initial market research and from there, decide whether it is worth it or not to proceed with this product. Then only you proceed to the next step. No point get all the costing when product no demand at all...