The employer files the petition and ordinarily pays the government filing fee and any related fees it chooses, such as premium processing; consult the USCIS fee schedule for current amounts. Relocation costs are a matter of company policy, not immigration law.
Ask for the cost split in writing before accepting
L-1A is an employer petition, so the company is the applicant before USCIS and the filing fee is a company expense in practice. The fee schedule lists the base I-129 charge and any additional statutory fees that apply to L petitions, and the employer may elect premium processing to obtain a decision within a fixed window. Beyond that, nothing in the regulation obliges the company to pay for moving, temporary housing, tax advice or the spouse's professional licensing.
Hypothetical example: a Lac-Beauport manager accepts a U.S. subsidiary role assuming the group will cover a cross-border tax accountant, only to learn that policy covers the immigration lawyer and nothing else. Before resigning from the Québec role or listing a house, obtain a relocation letter that states which costs the company bears, whether a repayment clause applies if the transferee leaves early, and how the salary will be paid and taxed.
Keep those business questions in the employment negotiation, not in the immigration file, which should contain only what proves eligibility.