Hi,
My name is Sneh, I am a certified trainer and consultant on AWS.
My day to day job includes assisting companies in migrating their environment to AWS and maintaining it.
I have just implemented a solution exactly to your requirement where a customer needed to scale up and scale down their AutoScaling group using Lamda, this solution should work for you as well with slight modifications.
I would need to know the triggers based on which you would like to scale up and scale down.
Feel free to ping me in case of any questions, if everything matches well, we can get this setup within 2 days as well.