Government filing fees follow the standard USCIS schedule regardless of the argument's complexity; the added cost is typically the time spent documenting the company's own procedures in detail.
The added cost is preparation time, not a separate government charge
USCIS does not charge a different fee based on how the specialized-knowledge case is argued, and the petition still follows the standard Form I-129 fee structure under the current fee schedule, Form G-1055, which should be verified before filing since amounts change. The practical cost difference in a case like this comes from the extra work of pulling together the company's internal welding procedure specifications, documenting the specialist's specific role in developing them, and writing a narrative that clearly distinguishes company-specific knowledge from industry-wide certification. That preparation work takes longer than assembling a petition around a role where the specialized-knowledge claim is more self-evident, but it is time spent on evidence quality rather than an additional government fee tied to the argument's complexity.