Design a standalone spreadsheet with variable outputs, which can also be embedded inside my word press site

My company makes renewable energy devices. We want to create a simple, elegant design of a Return On Investment calculator, something we can use as a stand alone, and embed in our wordpress site ([login to view URL]) for our customers to use. We then want to be able to see all the calculations they do. We are also considering hiring someone on an ongoing basis to help do an overhaul of our site, which is full of dead ends and unneeded content.