Don't shoot the messenger, but there is a lot of misinformation being spread in this thread, especially about what is legal or not. Ethical and legal are not the same, nor can be enforced the same.
You will find out that just about any merchant doing business online will have a disclaimer about pricing errors...and they can cancel the sale before shipping
(but not necessarily before charging your credit card) if discovered.
As a buyer, you may not like it, but there isn't really anything you can "legally" do about it beside telling the rest of the world. Many businesses who operate on a reputation standard, with do what is best and may try to honor a previous price even if it's wrong. This is just good customer service and smart for repeat business, but it's not legally required they do it.
Don't believe me? Case in point, and one of the best internet companies there is.....Amazon.
"List Price" means the suggested retail price of a product as provided by a manufacturer, supplier, or seller. We regularly check List Prices against prices recently found on Amazon and other retailers. Certain products may have a "Was Price" displayed, which is determined using recent price history of the product on Amazon.
With respect to items sold by Amazon, we cannot confirm the price of an item until you order. Despite our best efforts, a small number of the items in our catalog may be mispriced. If the correct price of an item sold by Amazon is higher than our stated price, we will, at our discretion, either contact you for instructions before shipping or cancel your order and notify you of such cancellation.
Other merchants may follow different policies in the event of a mispriced item.
We generally do not charge your credit card until after your order has entered the shipping process or, for digital products, until we make the digital product available to you.