Spend and cost have different meanings and usage. Spend refers to the expenditure of time and money and can only have a human subject. It can be used passively. On the other hand, cost refers to the expenditure of time, money, energy, etc. It can only have inanimate subjects and does not have a passive form. The differences between spend and cost are as follows:

1. The subject of spend must be “a person,” while the object can be money, energy, time, etc. It is followed by “on/for” + noun or an optional gerund form, and does not take infinitives. For example: He spent a lot of money on his new car.

2. Cost can be used to indicate the expenditure of time and money. Its subject is usually “an object” or “an action” and represents “expense” or “consumption.” For instance: The book cost him one dollar.