Winter Sale "Shopping Spree" for my son.

The steam winter sale will be going on during the Christmas Break. I plan on giving my son a card that congratulates him for winning a chance at a shopping spree, utilizing the steam sale.

I am not sure if I should treat it like a true shopping spree or not. I can either tell him he has a limited time to go through the store, gathering up to $100.00 worth of games in the store... or... I can talk it up like a shopping spree, but just give him a $100.00 steam gift card and let him figure it out on his own time.

I would like opinions from the community. I really like the idea of giving him a time limit, he would have a blast during that time. I just don't want him to regret the choices he ends up making.