The correct answer is $\boxed{\text{D}}$.
The manufacturing budget is the total amount of money that a company expects to spend on manufacturing its products in a given period of time. It includes the costs of direct materials, direct labor, and indirect manufacturing costs.
Direct materials are the materials that are used to make the product. Direct labor is the labor that is directly involved in making the product. Indirect manufacturing costs are the costs that are not directly related to making the product, but are necessary for the manufacturing process to take place. These costs include things like power, maintenance, and supplies.
In this case, the manufacturing budget is $20,000 + $5,000 + $10,000 = $45,000.
Option A is incorrect because it is the cost of only one of the three types of costs that go into the manufacturing budget.
Option B is incorrect because it is the sum of the costs of direct materials and direct labor, but it does not include the cost of indirect manufacturing costs.
Option C is incorrect because it is the sum of the costs of direct materials and indirect manufacturing costs, but it does not include the cost of direct labor.