We're re-building our e-commerce framework to improve overall performance, increase our flexibility, and specifically optimize our checkout flow.
Here's a little visual review of a wide ranging set of add to cart buttons.
In every case, the price is grouped with and located nearby the "add to cart" button.
This chunking produces minimal effort by the user for the multi-step process of check the price and committing to the buy. Understanding the (obvious in this case) user "task model" creates the realization that the user always checks the price if there's any chance of completing add to cart. By grouping the add to cart near the price, typically only separated from the price by product options, the site designers are confident that user will know where the affordance (an opportunity for action) is to buy.
The usability lab is almost ready -- we should be open for business on Monday and one of our first evaluations will be a series of add to cart layouts. Stay tuned.