Python Desktop App: Landed Cost / Quoting Calculator (Excel I/O, Tkinter GUI)

Project Overview We are a wholesale distribution business and need a Python desktop application that calculates landed cost per SKU for customer quoting. The tool ingests an Excel file (one row per SKU) filled out by non-technical staff, applies our contracted warehouse rate table and container/pallet packing rules, and outputs a results Excel file with per-carton costs, mode of shipment (floor-loaded vs. palletized), and a full audit trail. This is a fixed-scope build against the detailed specification below. All calculation rules, rate tables, and input/output formats are already defined — we are not looking for design consulting or iterative discovery. If the specification is unclear on any point, we prefer a written question over a call.