just labour + material?
I would guess 50 bucks if that much - basically a chinese girl sewing a piece of tissue for a couple of hours
but then for the sewing machine to exist it needs to be bought and then amortized into the piece price, same for the bench where the sewing machine sits, the facilities where that bench is located, then all the energy costs to have all these things running and so on and so on..
also - for the operator to get paid someone needs to process the salary, for the sewing machine to work needs to be maintained, etc., etc., and again you need to take into account all these indirect costs on top of just labour - call it SG&A or by any other name
to be honest i would be surprised if brands that do not have their own manufacturing facilities, most of them, know the price of the kit for material + labour only, as I am not seeing the 3rd party manufacturing partner to disclose their own business case
a different question is how much does cost a kite to a brand; do not have an answer but suspect it´s highly dependent on volume.
If you really want to know just go to www.alibaba.com
, contact a couple of sellers and get an idea about both the MOQ and the price.