Shouldn't be double in the long term. Think of the second cloud as a cold standby. Depends on the system. Periodic replication of data layer (object storage/database) and CICD configured to be able to build services and VMs on multiple clouds. Have automatic tests weekly/monthly that represent end-to-end functionality, have scaled tests semi-annually.
This is all very, very hand-wavey. And if one says "golly gee, all our config is too cloud specific to do multi-cloud" then you've figured out why cloud blows and that there is no inherent reason not to have API standards for certain mature cloud services like serverless functions, VMs and networks.
Edit to add- ink ow how grossly simplified this is, and that most places have massively complex systems.
This is all very, very hand-wavey. And if one says "golly gee, all our config is too cloud specific to do multi-cloud" then you've figured out why cloud blows and that there is no inherent reason not to have API standards for certain mature cloud services like serverless functions, VMs and networks.
Edit to add- ink ow how grossly simplified this is, and that most places have massively complex systems.