Instances 20 % of time active, 80 % inactive (no fees except disc space) with fixed pub

Hi there. I am looking for Linux instances (with fixed public IP on each instance) which I intend to pay for only when instances are active / on (20% of the time instances would be active, 80% inactive - so I pay hourly fees 20% of the time, 80% only disk space charges), but a fixed public IP is required for each instance (even inactive, the IP does not change when activating the instance). I am also considering using some solutions with an openstack and public IP block, so please let me know if such a solution is available on the OVH public cloud. I am also open to suggestions. I use VPS and a dedicated server for my solution but there is no flexibility (usually I need 15 VMs but there may be a situation where 25 VMs will be needed and the dedicated server will have no resources) Regards, Kris