@Jyotiranjan Mishra, I won’t say it is free.
• Building a database costs money, you can look out for
Apollo.io, Zoominfo to build those
• You would need to buy a paid plan for any email automation tool
• Tool to warmup the email
These are the two costs that would be there considering that design and content one can handle by themselves.
PS: Alternatively, you can send one on one emails by setting up automation via google sheet, but it is not a viable solution to look out for.