Do you have a table where each purchase is logged with the product ID, supplier ID, Cost and purchaseDate are recorded?
And do you have a relationship between your products table and this table that matches records by productID?
If so, you need only define the relationship to be sorted by purchaseDate in descending order. This makes the most recent purchase of that product the first related records.
From the context of Products, you can then just refer to fields of this related table and the relationship will reference the most recent transaction.