Setting a product's Purchase Price to be that of a Supplier is a three-step process.
1. Associate the product to one or more suppliers.
From the products list, click the supplier icon, next to the product you'd like to associate with a supplier.
and add the supplier or suppliers in the pop-up screen:
2. Once the product is associated with a supplier, you need to set a Supplier Price for that product:
There you can enter the Supplier Purchase Price and hit Tab - the new price will be saved automatically.
3. Now, all you need to do is to set the corresponding Pricing Rule to define the conditions under which that Price will be used. This is needed in order for this price to appear automatically when creating Purchase Order or Purchase/Receipt documents for that specific product. In particular, in the Edit/Delete Purchasing Pricing Rule, you need to set the Base Price as 'Selected Supplier Purchase Price'. This step needs to be done only once.
Now whenever this product is entered in a Product Order or Purchase Bill, the Supplier Purchase Price will be automatically retrieved.