I like the Idea if the guy splits the $100 between everyone who picks up the slack. and not pro rated. if theres four of you, you should each get an extra $25.

If its not like this, then he can skip out all the time and save $25 for not getting a sub.

or if everyone rotated, and skipped out. If this was a monthly project and there was 4 of you,each one of you could skip 3 months, out of the year.