In Finance -> Schedule of Rates you can set up as many sales rates as you want. So when a job is created for a specific contract, its associated schedule of rates will be selected. And the type of job, priority, site etc will then determine the specific sales rate it will select for the job from the associated schedule of rates. This sales rate is then applied to the number of hours worked on the job from the job visit. This then creates a sales value for the job visit which can then be costed as a new cost with its sales value.
Create your Client Schedule or Contractor Schedule and then create the rules associated to them.
You can also define the cost or sales rate which is then applied to the job visit hours to determine the total cost or sales value. Typically this is an hourly rate. But you can change the time unit rate to charge by the half hour. There are additional advanced settings. For example if you want to enforce a minimum charge for the job based on number of time units.