1. A computer-implemented method for dynamically setting prices for tasks in an electronic marketplace that facilitates transactions between task requesters having tasks available to be performed and task performers able to perform tasks, the method comprising: receiving indications of multiple groups of tasks to be performed by task performers, each group having multiple related tasks and an associated desired pace for performance of the tasks of the group; for each of the multiple groups, automatically determining one or more initial prices to be paid for performance of at least some of the tasks of the group, the one or more initial prices being based at least in part on the desired pace for the group, the automatic determining being performed by one or more configured computing system processors that provide the electronic marketplace; after performance of the tasks of the group by task performers has begun, automatically monitoring an actual pace at which the tasks of the group are being performed; and while at least some of the tasks of the group remain to be performed, if the actual pace at which the tasks of the group are being performed differs from the desired pace for the group by more than a threshold, automatically modifying one or more prices to be paid for performance of at least some of the remaining tasks of the group, the automatic modifying being performed by the one or more configured computing system processors to alter an actual pace for performance of the remaining tasks of the group in order to reflect a desired pace for those remaining tasks of the group; and for at least one of the groups of multiple related tasks and while at least some of the tasks of the group remain to be performed, dynamically adjusting the desired pace for performance of remaining tasks of the group to account for deviations between the actual pace at which the tasks of the group are being performed and the desired pace.