The filing fees are those published in the USCIS fee schedule, Form G-1055, which is the only figure worth relying on because amounts change. Premium processing is optional and adds to that. The substantial cost is preparation: corporate records, charts, letters and legal work.
Assembly is the expense; filing is the invoice
A transfer petition is a documents project before it is a form. Producing a clean ownership chain may require a corporate lawyer to reconcile registers that have not been updated in years. Organisational charts have to be drawn for two companies and reconciled with actual payroll.
A support letter that survives scrutiny takes several drafts and, sensibly, professional review. Where the American entity is newly formed or recently acquired, add evidence of premises, capitalisation and operations. Against that, the filing fee itself is straightforward, and the fee schedule is the reference to check rather than any figure quoted in conversation.
Employers frequently underestimate the internal time involved: the finance manager, the controller and the transferee's own supervisor will each spend real hours on this, and pretending otherwise is how deadlines slip.