The employer files Form I-129 with the L supplement and pays the government charges published in the USCIS fee schedule, Form G-1055, together with any premium processing it elects. The larger expense is preparation: assembling corporate evidence, and where necessary reorganizing reporting lines before the petition is written.
The bill is mostly professional and internal, not governmental
Because an L petition is an employer filing, the cost question is really a budgeting question for the business. Government charges are set out in Form G-1055 and change from time to time, which is why that schedule rather than a quoted figure is the right reference. Around it sit costs the company controls.
Corporate evidence has to be gathered from lawyers, accountants and registries in two countries, and a group with an intermediate holding company will spend real time producing a chart that survives scrutiny. If the operations directorship as currently defined does not support the branch being claimed, the honest response is to fix the role — reporting lines, budget authority, formal ownership of the maintenance function — which has organizational consequences and cannot be done in a fortnight. Counsel's time is spent chiefly on that structural question.
A refused petition costs the filing again plus the delay, and a business that has already sold the transfer internally pays for that twice.