To be able to make money on resold instances you need to bill your customers hourly based on their instances usage and sizes.
With HostBill you can define Flavors - sizes of virtual machines that customers can create, based on Amazon EC2 instance sizes (ie t2.micro). Flavor manager plugin located after activating in Extras → Cloud Flavor Manager allows you to setup hourly usage price per each flavor customer uses. Flavors defined by staff members are visible in client area during new VM creation - customer sees hourly and monthly price for VM, and Flavor description. Your clients will be able to create virtual machines - limited by total count of them under one account. Charge for each machine that is powered on is calculated every hour to the next bill - based on the size that customer has chosen to use. After month of usage customer receives invoice with list of virtual machines and their usage (number of hours and total charge). Even if customer is to remove their virtual machine after period of time - it will be still visible in the next bill details.