That all depends on the structure of the tables, which I am not getting.
I would have a product table, and a current price and sales table, then do my reports by filtering for month. It sounds like you have one table that has a product with its current price and current sales figures only - basically the query results you want from a more normalized structure.
I would pass the data to the archive table, then using where month = current month - 1, populate the fields with that data in your update form. Then push this back to the Sales table.
Really, Sales should look up to Products, and Product information should not be in the Sales table.
ProductID - PK
ProdDesc - text
SalesID - PK
ProductID - FK
CurrentDate - Date (for the Month)
Then selec the Product, and the sales where currentdate("m") = the current month, etc.
Anyway, what specific code do you need? I would need your field names and table names.
Did that help any?