Estimates are based on a sample of the text. Cost is directly related to the complexity and density of the material, plus its length. These are really just concordances or lists of words, not indexes. They do not deal with relationships and concepts. Information is not gathered in one location so readers may easily miss many references.
Problems result from numbers, symbols, titles, abbreviations, acronyms, misspellings.
Page ranges are not available. These are very practical for publications that are revised frequently. The procedure is awkward, time-consuming, and the complex formatting of entries slows down the indexer. It is often just as fast, and a better index results, if the index is first created with dedicated indexing software and the terms then embedded into the text. This is because embedded indexes can be viewed only by generating them, not as they are being created.