The government charge depends on the route: a Canadian citizen applying at a port of entry pays a modest processing charge, whereas an employer filing Form I-129 pays the petition fee on the USCIS schedule. The larger and less predictable costs are usually the private ones — credential evaluation, translations, legal review and travel.
Budget the private costs, not just the government ones
Check current government amounts on the USCIS fee schedule rather than on any figure quoted to you second-hand, since those amounts change and a stale number is worse than none. Then list what the schedule does not cover. Hypothetical example: an accountant at a Saint-Cyrille-de-Wendover commercial printer is told by her prospective employer that the company will handle the fees, so she pays for a credential evaluation and books non-refundable flights before the offer letter is finalised; the letter then arrives describing a job title her chosen Appendix 2 entry does not support, and the money spent on travel is gone.
Agree in writing which side pays for the petition, the evaluation, translation of any French-language credential, and legal advice, and agree what happens if the start date moves. It is also worth remembering what money cannot buy here: a fee does not make an unlisted occupation eligible, and paying for speed does not improve a file whose weakest element is the description of the duties.