When is AWS Lambda More Expensive Than Heroku?

I was talking to a friend of mine yesterday, and he mentioned that his company had a Django app deployed on AWS Lambda. I asked why, and one of his main reasons was that it's cheap.That got me intrigued - a Rails-like webapp, on Lambda, and it's cheap? Could that really be the case?To get my biases out front: I think most developers choose Lambda when what they really wanted was autoscaling on EC2 or Heroku. However, I'd like to lay out the case here that servers can be cheaper than serverless, and why that's the case.Our example scenario will be a typical web application:250 millisecond response times10 requests per second (600 requests/minute)Uses about 256MB of memory per processSince Lambda only does your "computing", we'll just compare computing costs alone. So, we're talking about Lambda costs versus Heroku web dyno costs.