Expect legal review time for two agreements rather than one, possible credential evaluation or translation depending on where the degrees were earned, and the usual costs of the chosen route. Confirm current government fees directly, since they change independently of any individual case. Allocate cost the way you allocate responsibility. An entity that must produce and reissue letters absorbs administrative time; the applicant absorbs what attaches personally, such as a credential evaluation. Agree in writing who pays for what before either side commissions work; neither can bill the other by assumption.
Budget for the review, not just the filing
Sorting out which entity employs the professional often takes more counsel time than a single-employer case, because the documents must be read against one another and are sometimes reissued. If the appointment depends on a foreign degree, an evaluation may be advisable; note that translation and credential evaluation are separate services with separate costs. Ask which of the two organizations is paying for what.
Advisers outside the case add cost nobody budgeted. A relocation firm, a departmental coordinator or a recruiter may each produce paperwork, and duplicated or inconsistent versions then have to be reconciled by counsel at the applicant's expense. Ask the organizations to route documentation through one named contact.
Government charges also differ by route, since a request at a port of entry and an employer petition on Form I-129 do not carry identical costs; confirm current figures from the official source rather than an internal estimate.