Hello Howard,
I think Ariba buyer would not be a right place to know if you are getting a best price because in Ariba buyer we only maintains the suppliers with whom we are already in contract and already purchasing goods from them. Hence in a way with Ariba Buyer we are only working on a small group of suppliers though there are many suppliers available in the market who can offer you better price. Probably Ariba Discovery is the solution to your query where you can search for all suppliers in your geographical region which are dealing with the product you are looking to purchase and can also compare their prices. Below is the link for Ariba discovery which is much similar to any e-commerce site and easy to use.
https://service.ariba.com/Discovery.aw
Once you are satisfied with the offerings of a supplier, you can setup him up in your Buyer and place orders for the same.
Amit