At the port of entry, the applicant pays the TN application fee collected there. If the employer files Form I-129 instead, the petition fee in the USCIS fee schedule (G-1055) applies and premium processing is optional. Translations and any credential evaluation are private costs.
Two government paths, one set of private costs
A Canadian citizen has two ways to obtain TN. Applying in person at a port of entry involves the fee collected by U.S. Customs and Border Protection at the time of admission, and the admissibility decision is made during that inspection rather than on a guaranteed timetable.
Having the employer file Form I-129 with USCIS in advance involves the petition fee in the current fee schedule and, if speed matters, the optional premium-processing fee; the applicant then presents the approval notice at the border. The private costs are the same either way: certified translations of the diploma and transcript, a credential evaluation if the degree is foreign, and any advisory fee for preparing the letter and package. Confirm with the employer in writing which costs it will bear.
Nothing about the sales question changes the fees, but a refusal at the port of entry means the fee is spent and the record of the refusal follows the applicant, which is why the letter should be right first.