I'm about a third of the way through indexing the book—that is, entering all my highlighted elements into an alphabetized document—and I figure I'm working at the rate of about ten pages a hour, twelve when I'm doing well. That's not bad at all, but I'm sure not going to get rich doing this.
My drummer-colleague in the history department as a 900-page manuscript he needs indexed; he tells me he's contacted an indexer who'd do it for $1.50 a page; which seems rather low—this page recommends expecting between $4 and $6 per page for an academic book. Even if we take that top number ($6) and my fastest rate (12 pp. an hour), we need to figure in probably at least as much time spent going over the proofs in a preliminary fashion. So 6 pages an hour, all told, at $6 a page = $36 an hour.
That seems like an impressive number, or at least it would have when I was eighteen. These days, in white-collar land, I feel like I might be working beneath my normal rates. On the other hand, I'm going to come up with an index that I can truly call my own.