Billy, what you describe is not something we currently offer, but you may also be misunderstanding how the spot price works. It's very similar to ebay in that you enter your max price, so if you enter $0.10/hr and the spot price is $0.04/hr you will only pay the latter $0.04/hr. You should thus enter the max price you're comfortable with. What Amazon doesn't offer is to say "please convert my instance to an on-demand when the spot price exceeds the on-demand price". You can put all your data on an EBS volume and relaunch the server as an on-demand server from that volume, but that's not a transparent operation. We are working on schemes like that, but focused on arrays of servers rather than individual ones.