Shipping issues. Or my being dumb

Hi, im trying to sell low priced items on Amazon and shipping FBM (I do shipping) but I’m running into a small problem. I can only buy shipping once I make a sale, so I only know how much shipping will be then. But I need to know how much shipping costs do I know how much the shipping cost needs to be. But I can’t because the payment is made before. So Amazon sets an average shipping price. But what if that averaged price is not enough for my shipping. I cannot include shipping price into my product price because my product only costs 4.99 so adding 9 bucks or something on top of that will destroy the listed price and no one will buy it because it looks outrageously expensive. So what do I do?