Budget the government fee for the method used, any credential-evaluation charge, travel to the port of entry and professional advice. Fees are published in the USCIS fee schedule and should be checked at the time of filing.
Price the method, then the paperwork
A Canadian citizen can present the TN application at a port of entry, where the applicable fee is collected on admission, or the employer can file Form I-129 with USCIS in advance; each has its own fee in the USCIS fee schedule. Beyond that, the real costs are preparatory. A credential evaluation for a non-North-American degree is a separate charge, certified copies of designation records may cost a little, and if the U.S. employer wants counsel to draft the letter, that is a professional fee. Ask the customer whether it will reimburse these and get the agreement in writing before spending. Do not include relocation costs in the immigration budget as if they were conditions of approval; they are household expenses that depend on the outcome, not inputs to it.
Hypothetical example: a Canadian pharmacist receives a U.S. offer that includes reimbursement for immigration preparation. The first review should make a two-column budget: employer expenses tied to the offer and personal expenses such as travel, housing and licensing. The signed offer or reimbursement policy settles who bears each charge; a verbal assurance does not. The applicant should also check whether the chosen process is a border request or an employer petition, because the responsible party and government charge can differ. None of those payments cures a missing professional qualification or state practice requirement.