We currently pay somewhere between 85-100 USD on a monthly basis for RDS usage. But most of the times we don't access our database instances. Is there a way to reduce the billing by bringing down the instance or go in for a shared database mode. What kind of alternatives exist?
You can delete an instance at any time with DeleteDBInstance. By default, a final snapshot will be created . Then, you can recreate it at a later time. See this FAQ. The final snapshot storage cost is $0.15 per GB-month.