Even I faced the same issue but later my friend suggested me a solution for this issue.
I'll explain to you how did I solve this problem in a step by step manner.
If you limit your Hadoop cluster nodes only to t2, micro instances and total EBS volumes size to 30 GB, then you can run a Hadoop cluster within the free tier. Do note that the hardware on t2.micro is of inadequate.
The information about free tier on AWS is that you are allowed only t2.micro for 750 hours per month. That means you can run for example 10 nodes for 75 hrs in a month for free after which you would be billed.