Competitor price parser with daily report and alerts

We sell a catalogue of several hundred products and constantly lose margin because we react to competitor price moves too late. We are looking for a developer to build a parser that regularly collects prices for our matched items from a fixed list of competitor pages and turns that into numbers we can actually work with, without anyone copying values by hand.

The script should run on a schedule once a day, gather the current price for each tracked product, and write the results into a structured spreadsheet: one row per product, columns for each competitor, the date, and our own price for comparison. History must be preserved, so we can see how a price moved over weeks, not just today's snapshot. If a page layout breaks or an item goes out of stock, the run should record that clearly instead of writing a wrong number or silently skipping the row.

The part that matters most is change detection. When a competitor raises or drops a price beyond a small threshold, or an item that was unavailable comes back, we want a notification with the product, the old and new value and the difference. We are open to a sensible stack; reliability and honest error reporting are more important than speed. Please include a short setup note so we can add or remove tracked products ourselves.