Hello there!
I'll be honest with you, simple scripts do not take 500 lines of code. So you are way below the budget it might require. I'm saying might simply because it might in fact be easy to do what you need.
VBA sometimes is a lot more complex then Google Apps Script. I am honestly not very strong at VBA, but I'm good at GAS. SO if you want to give me a bit more details of what the script does and show me the script itself, I might be able to tell you how difficult it will be.
I should say however, that there is no adopting the script, you will need it written from scratch. Different languages and all that.
Anyhow, let me know if you wish my help.
Cheers,
Denis