See previous Chore Chart post here.
What I did was take off all the chore stickers off the wooden pieces and just put on labels that all read $0.25. So now when he helps me (does chores) I tell him how much money he can put it that days column. That way it's not limited to just a few items and I can attach an amount that is deserving of how much he really helped. It's been working much better!