No you can't. Not always. Their are always people that can not be "bought", their is always someone who is not willing to sell their land at any price, some soldier will not fight for an unjust cause, some wizard who will not sell their services.Money can be used to buy magic. Or loyalty. Or military might. Or land. Or politicians. Or...
Money is power because, like any other kind of power, it can be converted into whatever type of power or resources needed for a situation.
And if you disagree with me, then using your own example, you might as well say "Sheep are power" because with sheep I can make food, and clothes, and with food and clothes you can trade for...x.
EDIT: Give me sheep and I shall rule the world!
Sure, money can be used to exert power, sometimes. But it is not the same thing as power itself.