That means it would cost you $0.50 / million requests. AWS Lambda would be $1.84 / million, $3.50 / million for API Gateway, $0.40 / million for AWS Route 53, and various other charges.
Originally we were thinking about it in those terms (as an alternative to Lambda@Edge), but based on our recent results I am happy to have people compare it to Lambda as well. Lambda with API Gateway is at least eight times more expensive than Workers, and only runs your code in one location instead of 151. Unless you're using Lambda to do something ultra-Amazon-specific (like process S3 changes), I don't see why it would be the better choice.