Support is priced at an annual contract of 10% of the cost of a project. This is a relatively basic method for gauging the complexity of an application.
As an example, consider that an application cost $42,000.00 to build, a typical minimum viable product, or first shot.
10% of $42,000 would be $4,200 for an annual support contract. This comes out to around $350 a month which for an application of this size would take 2 - 3 hours a month of maintenance.
Now, imagine that the business is growing, and the total cost invested into the application has reached $120,000. Business has grown and so has the app. Now the 10% is $12,000 a year or $1,000 a month. This equates to 8 hours a month of maintenance.