Lambda static outbound IP address without NAT gateway

My lambda use case deals with outbound connections. I would like to have a static IP address, so I can whitelist them.

Since my use case deals with outbound connections, I can't use a load balancer here.

NAT gateway can be associated with elastic IP address. But cost is a barrier.

At the moment, I'm using a NAT EC2 instance for having a static IP address.

Is there a better way?

p.s. My lambda function is triggered by SQS. And my function require access to S3 and DynamoDB. No other access required.

Edited by: Vir2020 on Jun 2, 2020 1:19 PM