In a game I just finished, with escalating spoils, the rewards were as follows (from the game log):
4, then
6, then
8, then
10,
then by 5's to 100 (eg. 15, 20, 25, etc)
then increasing by 5 more with each set handed in (eg.
100, then plus 10 to
110, then plus 15 to
125, then plus 20 to
145, then ...