Here is the link to the Amazon revenue calculator for estimating fees. Find a similar product to use to get an estimate of your fulfillment costs and fees.
When I send shipments into the warehouse it usually runs .30-.35 cents a pound to ship buy UPS purchased through Amazon. This is what your will pay to get the product to Amazon for FBA
Grocery is a gated category that requires approval to sell in. Are you approved to sell in grocery?? Thats a major issue. If you are not approved to sell in grocery you need to look at all the requirements and see if you can even get approval first.
The buy box is in the upper right hand corner of almost all listings on Amazon. This is what customers usually use to purchase a product. Amazon uses a complex algorithm to choose which seller has the buy box. Having the buy box is a huge advantage for a seller.