New buyers of Google Cloud System are suitable for just a $300 free demo. Jogging by this codelab should not cost you more than a few pounds, but it may be more if you decide to use more sources or if you leave them jogging (see the "cleanup" part at https://azure-support23332.blogdanica.com/26124518/the-basic-principles-of-linux-postfix-mail-server-setup