This method is based on the default [GroupRegPos] field, which is calculated for each participant in a group registration.
During a Group Registration all participants will be assigned the same value for [GroupID] and then are numbered starting from 1 in the [GroupRegPos], corresponding to the order in which participants are entered in the form.
To assign different entry fees based on [GroupRegPos], use the filter in the entry fee settings.

In this example - an entry fee of 10 EUR will be applied to the first two participants in the group, and then for the third participant and above an entry fee of 5 EUR is applied.
