1) TANSTAAFL means that nothing is truly free - there is always a cost associated with something, even if it is hidden or distributed among society. 2) Examples of hidden costs include imputed interest costs from tying up money that could otherwise earn interest, and imputed depreciation/appreciation of assets over time. 3) Relative prices compare the price of one commodity to another (the base), and can help simplify cost-benefit analyses by showing the relative costs of alternatives while holding the benefits constant.