I reject this framing. There is more to life than dollar value. Petty thiefs destroy social trust and cohesion, and this destroyed trust has bigger value than the value of items they stole.
Additionally, remember that the goal of prosecution and punishment is to deter crime, and so you should not only consider the cost of prosecution vs the cost of stolen item, but also the cost of all the crimes you enable when the thieves learn there is no punishment for petty crime.