I have experience on using Python for batch CSV processing, and I'm familiar with databases & SQL, including PostgreSQL. I'm sure I could complete your job within specified timeframe and provide you with proper and professional solution.
I pay serious attention to the quality of code I produce, keeping it clean and clear, so I think you could easily understand what's going on and alter the script behaviour on your own.
Sure after the script is done and you're convinced it works as you've expected, we'll choose an hour to make a code review, and I'll answer your question about how the script works.
As your description doesn't contain much details about the job, I reserve the right to reestimate the bid and due date, if the scope of work is bigger than I assume.