The employer bears the petition costs, which include the USCIS filing fee for Form I-129 with the L supplement, any fraud prevention and detection fee that applies, and premium processing if requested. Current amounts are published in the USCIS fee schedule, Form G-1055.
Budget for the evidence build, not only the filing
Filing fees are predictable and published; the rest of the budget is not. Restoring a dormant subsidiary to real operations means a lease or yard agreement, operating authority, insurance, and accounting work to produce clean records, and none of that is an immigration expense in the company's mind until it is needed for the file. A new-office filing shifts spending forward instead of removing it, because the premises and the staffing plan must exist before the petition rather than after.
Professional costs then cover the corporate review, the drafting of the managerial description, and preparation for a request for evidence, which is common where activity is thin. Fees change on their own schedule, so confirm them on Form G-1055 immediately before filing rather than relying on a figure quoted last year.