The easiest way to create a legal document for free is to use a form. A durable power of attorney is no exception. Many sample forms are available online (see Resources below), and it is a simple matter of adjusting a form to fit the details of your situation. Generally, a power of attorney gives an agent the right to act on a grantor's behalf in certain situations. Those situations can be narrow and specific or quite broad, as designated in the power of attorney document. Power of attorney only lasts while the grantor consents to the arrangement and will cease if she becomes incapacitated by illness or death unless the power of attorney specifically grants authority in those situations. This is what it means for a power of attorney to be "durable." Giving someone the authority to act on your behalf in the case of a coma or mental illness can be an important part of estate planning, but it needn't be costly.
Choose a form. Take the time to peruse several different durable power of attorney forms and select the one that is closest to the arrangement you'd like to make. If you are granting sweeping authority in virtually all situations to a very trusted person, a short form should suffice. If, however, you want to very narrowly tailor the authority of your agent without unnecessarily binding her ability to function on your behalf, a longer, more detailed form is the appropriate starting place.
Consult with your agent. The legal document only codifies what should be an explicit understanding between yourself and the person to whom you grant power of attorney. Not only should she be willing and able to accept the responsibility, she should know in advance your wishes for all possible contingencies, and she might have some valuable input. The ultimate agreement is what will constitute the durable text of the power of attorney document.
Identify the parties. No matter which powers are being granted, an essential element of a power of attorney is to adequately identify the people involved. The grantor and agent should be described by their names and addresses. If the agent is a legal or financial planning professional, it is possible for her to use her business address. If you are designating her corporation as the agent, using the tax ID number is also suggested.
Identify a jurisdiction. The laws that control the interpretation of the document can be based on where it is signed, where the agent resides and where the grantor is located when incapacitated. Though not absolutely binding, setting forth the intention for the document to be governed by the laws of a particular jurisdiction makes it easier to control how a power of attorney will be used. In most cases, the intended jurisdiction is the state and county of the grantor's primary residence.
Modify powers and restrictions. Using your chosen form as a guide, work through each enumerated power and alter the language to reflect the specific intentions of the grantor. If no power is granted in a specific area, parts of the form can be crossed out entirely. Others can be altered and made more specific.
Retype the form. If the form has been altered, which is most likely the case unless a very short and broad form is being used, it should be retyped so as not to indicate any stray or untidy marks.