A couple of notes on this technique:
When you're reviewing item prices, feel free to use prices published on vendor websites. If the item doesn't line up 1:1, be prepared to discuss how the items are substantially similar and how the differences between the items lead to price differentials. For example, if the item used as a basis for comparison has more functionality or enhanced performance capabilities than the item being purchased, the fact that the purchased item is offered at a lower price is not necessarily dispositive of fair and reasonable pricing.