eBay Listings Export & Import Guide

I need to move everything from my existing eBay store over to a brand-new account and I want a process I can repeat on my own next time. I currently keep all listing data in spreadsheets (Excel/CSV), so the solution must revolve around that format rather than third-party listers... (Budget: $10 - $30 USD, Jobs: Data Management, Documentation, eBay, Excel, Inventory Management, PHP, Process Automation, Software Architecture)