The new pricing page for lambda ("Example 2") shows the cost for a 100M invocation/month workload with provisioned capacity for $542/month. For that same cost you could run ~61 Fargate instances (0.25 CPU, 0.5GB RAM) 24/7 for the same price, or ~160 instances with spot. For context I have ran a simple NodeJS workload on both Lambda and Fargate, and was able to handle 100M events/mo with just 3 instances.
Serverless developers take note: its time to learn Docker and how to write a task-definition.json.