In the USCIS fee schedule and the published port-of-entry fee information. Amounts change, and a figure quoted in an article is not a source you can rely on.
Read the schedule, not a summary
Government charges for this category are modest compared with the categories that require petitions, but the exact amounts depend on whether the request is made at a port of entry or through an employer petition, and they are revised from time to time. The reliable practice is to open the current fee schedule at the time the request is actually being made rather than relying on a number that circulated last year.
Beyond government charges, a household should plan for the real costs that no schedule lists: credential evaluation where a degree was awarded outside North America, licensing or registration in the destination state where the profession requires it, document retrieval from institutions, and any professional review of the file. Those often exceed the filing charges.