Duplicate professional support, mainly. Expect accounting in both jurisdictions, corporate filings for each entity, cross-border tax advice, currency conversion on transfers, and travel that is frequent rather than occasional. These sit outside the invested capital and outside the immigration fees. Confirm official government charges for the chosen route when each step arrives rather than budgeting from an old figure.
Decide who pays for what, and from which entity
An adviser's invoice paid by the foreign company for work benefiting the U.S. enterprise creates an intercompany item somebody must explain. Agree the paying entity for each category before the invoices start.
Ask for a scope that separates structuring advice, evidence assembly, application preparation and any later response work, and ask what remains payable if the review concludes the structure needs changing first. That answer usually reveals how the adviser sees the case. Add one further category to that allocation: the cost of keeping the two sets of records separate enough to be readable.
A two-country structure generates bookkeeping that a single business does not — intercompany balances, transfer documentation, two sets of professional advisers, sometimes two currencies — and someone has to maintain it in a form that a reviewer could follow. Budget that work as an ongoing item rather than assuming existing arrangements will absorb it. Hypothetical example: an investor operating a calibration services business in one country and opening another assumes the existing bookkeeper will handle both, and the resulting single ledger, with entries in two currencies and no consistent treatment of intercompany items, has to be unpicked at a cost well above what a proper arrangement would have carried from the start.