Currently I'm on a state that testing costs me money and a lot of time...

Background: I'm deploying VMs at softlayer and using a post-deployment script(bash) that will install every software that I need after the VM is ready. The problem is, I can only test this script by deploying one VM, and it's currently taking around 4h for the script to finish... So every change that I make I need to create a new VM(costs money) and wait for around 4 hours to see if the script is broken or not... This is becoming chaotic and I won't be able to move forward if I stay this way.

I need a new way to approach this kind of situation and be able to test the provisioning script more quickly and without needing to deploy a new VM every time.

Do you guys know some tool to help me on this scenario ?