Codicils vary in cost depending on how much you need to change in your will. Most codicils that make a minor change or adjustment are relatively inexpensive at around $100. However, the more changes you need to make or the more complicated your will already is, the more you should expect to pay.
At the same time, if your codicil is simple and you can fill out a blank codicil form, it will probably cost less.
Past a certain point, your lawyer may recommend changing to writing a new will because that may be the cheaper and more efficient option.