The Form I-129 filing fees are published in the USCIS fee schedule, Form G-1055, with premium processing available separately. The predictable additional cost is evidentiary: offsite specialised-knowledge petitions are questioned often, and answering well means preparing the contracts, itinerary and knowledge evidence before filing rather than after.
Pay for the record first, because the second round is dearer
Two features of this petition raise its expected cost. The knowledge claim has to be built from internal material that nobody has previously organised: design records, commissioning reports, training documents, and an explanation of how long the company needs to develop a replacement. The placement issue has to be answered with contracts that may need renegotiating with three separate yards, each of which has its own commercial preferences.
Both are cheaper before filing. A request for evidence arrives with a deadline, and rewriting a shipyard agreement under a deadline gives away negotiating position as well as money. Premium processing shortens the wait but does not lower the evidentiary bar.
It is also worth pricing the alternative honestly: if the retrofit work is genuinely a service the subsidiary sells, some of it may be deliverable through short business trips or by a different structure entirely, and comparing those costs is part of the decision.