Python Script - for the merge 3 excel sheets

A client has found a new supplier and would like to populate his ecommerce store with their products, i've reviewed the data sheets that come via FTP (daily) from their supplier and they have 3 excel sheets - one contains products information, the other contains price/stock then last contains promo prices.

I would like to have a script made so that there is one main excel sheet that outputs as a CSV UTF-8 file but it needs to be able to match up rows by us choosing a unique identifier (in this case it'll be "model number") and then add columns into the matching. Leaving us with 1 CSV that has all the information from the 1st sheet and columns added for images, prices etc allowing me to process the feed through their ecommerce platform.

Will send over the excel sheets and explain some more when i have evaluated the proposals.