SQL Server using Parallel Plan for Cost less than 5
This can be confusing when you're first looking at parallel plans. The thing to keep in mind is that the cost based optimizer picks what it estimates will be the cheaper query to execute. It's not always right, but hey, it's not rocket science.

As a simple example, here are two count queries. One is allowed to go parallel, the other is forced to run serially.

SELECT COUNT(*)
FROM dbo.Posts AS p;

SELECT COUNT(*)
FROM dbo.Posts AS p
OPTION(MAXDOP 1);


Their query plans have the information we need:





The serial plan costs 121 query bucks, and the parallel plan costs 69.