It depends on the route, and the current government amounts are published in the USCIS fee schedule rather than quoted in conversation. The spending that changes outcomes is narrow: a credential evaluation where one is required, certified translations, and one early review of how the duties are described.
Separate government charges from preparation
Presenting an application at a port of entry as a Canadian citizen and having an employer file a petition are two different transactions with different charges, and the employer usually decides which one happens. Check both against the published schedule on the day, because amounts move. After that, the discretionary budget is short and worth spending well. An evaluation is worth paying for when the entry’s credential came from outside North America. A certified translation is worth paying for when records are in French. Advice on wording is worth paying for once, before the letter is issued rather than after an officer has read it. A thicker file does not repair an activity that falls outside the entry relied on.
Hypothetical example: a structural engineer from Roxton Pond is engaged to run the design and code-compliance work at a roof-truss and wall-panel plant in the United States, and a service offers an expensive preparation package before the employer has finalised anything. Build the budget in two columns: unavoidable charges on one side, optional professional help on the other, and a go or no-go date beside each. The records the employer can produce at no cost — the letter, the identity of the signatory, the reporting arrangement — belong in the first column of work, not the second.