The petitioning entity pays the government fees on the current USCIS schedule and its own legal costs; which company that is depends on who files. Travel, per-diem and site expenses follow the commercial agreement between the affiliate and its customers, not the immigration rules.
Separate petition costs from commissioning costs
Hypothetical example: a Haldimand County conveyor manufacturer and its U.S. affiliate disagree over who funds the L-1B for the controls designer who will commission installations at customer sites. Immigration law fixes only the mechanics: a qualifying U.S.
entity files Form I-129 and pays the filing fee, the fraud-prevention fee, any applicable statutory surcharge and premium processing if chosen, all at the amounts on the current G-1055 schedule. Legal preparation is negotiable between the companies. The larger costs are operational: flights, accommodation near customer sites, vehicle, tools, and the designer's salary while she is deployed.
Those are decided by the intercompany services agreement and by what the affiliate charges customers for commissioning, and they should be documented, because the petition must show the petitioner remains the employer paying and controlling her. A written intercompany agreement that allocates costs and confirms supervision serves both the finance department and the immigration file. Do not let cost negotiations produce a structure where the customer effectively employs her.