Techniques are described for facilitating interactions between task requesters who have tasks that are available to be performed and task performers who are available to perform tasks, such as for use by an electronic marketplace for the tasks. In some situations, the electronic marketplace automatically determines prices to be paid for performance of tasks, such as in accordance with pricing-related criteria specified by task requesters who submit groups of numerous related tasks to be performed. Such pricing-related criteria may include various types of information about a desired pace of task performance for tasks of a group, and if so the electronic marketplace performs the automated price determination in such a manner as to accommodate the desired pace, such as by dynamically modifying prices when monitoring of an ongoing actual pace of performance of tasks differs sufficiently from a desired pace of performance.