Attention: I'm not a teacher.
Hi…..
There are some more details concerning the matter in question.
To sell smth. at cost = to sell smth. at cost price
the cost price of an article, the cost price of producing it or the price at which it may be bought wholesale
cost price = the price paid by a merchant for the goods he buys for resale. / a price that represents the bare cost of production, without anything added for profit.
with cost = liable to pay costs (yielding profit)
at the cost of = at the loss or expense of;
at all costs = at all prices = whatever the cast may be
Regards.
V.