There are so few clouds, that it doesn’t work like this. When I saw it first hand the way it was done is prices were set to match competition. Occasionally somebody would reduce the prices, and others would match it. Since offerings are not exactly the same, there are variations, but overall for basic services like VMs and storage neither cloud will give you significant advantage in price.
Even if Google’s prices were half that of Amazon’s, it’s really hard to quantify the savings since the platform offerings are not identical, plus engineering switching costs could easily outstrip a company’s yearly cloud costs.