SQL Instances on VM Azure

Hi,

We have a requirement to run multiple SQL instances on a single Azure VM.

I know there is a SQL Server installer on C: but when I try running it it asks me for the serial number. 

My questions is how can I get additional instances running on a single Azure VM and what are the costs implications of running say for example 3 instances on Pay-as-you-go plan?

Thank you,

Henryk