1. The developer sets up some requirements: number of instances, X amount of CPU power, Y amount of memory, Z amount of storage, B amount of bandwidth, or other characteristics. These requirements are sent to the third party.
2. Cloud vendors (the "bidders") receive the characteristics needed by the developer. Each of them bid by providing a price per hour for the given characteristics.
3. The bidder with the lowest price wins the auction, sends back credentials to start deployment
4. The developer can start the deploy with the infrastructure provided by the lowest bidder!
All this may happen in less than one second, similarly to the auctions that happen when advertisers bid for displaying an ad when someone visits a webpage. This would need a massive standardization across cloud vendors, a system of penalties when the infrastructure provided by the bidder does not satisfy the characteristics, etc.
This does not too far fetched to me. It also make it easier for new cloud providers to start selling, and lower prices for developers.