A Buy Now price isn't required for items that have online bidding.
There is more than one school of thought about how to price Buy Now items. It really depends on the item, and on the buying power of your bidding community.
One approach is to set the Buy Now price between 25% and 50% above the established value. In doing so, a bidder will pay a premium price to remove it from the bidding pool.
Another approach is to set the Buy Now price between 10 and 20% below the established value. As long your profit margin meets the item cost, you become protected in terms of cost/value while the bidder feels like they are getting a bargain.