I have a 3 year old son. I started a "good boy" jar for him and every time he does something good (uses manners, picks up his toys, nice to his baby sister etc) I put money in his jar.
This has also made a huge change in his attitude as well.
Instead of being punished all the time for things when hes naughty, I reward him when hes good.
This makes him feel like a "big boy".
I also ask him what is one thing he wants, such as a toy.
Then, since hes so young and his attention span is so short, usually at the end of the week I take him to get his toy( no matter if he has enough or not).
Hes kind of young to teach him the actual value of money, but I feel that this shows that when you want something you have to work for it.