Mostly internal time. Government charges are set out in the fee schedule; the real expense is the engineering and records work needed to evidence what the employee actually built.
The expense is reconstruction, not filing
Confirm government charges against the current fee schedule when the petition is prepared, and treat premium processing as a separate decision with its own cost. Those are the predictable amounts.
What a small operation underestimates is the internal effort of assembling evidence that was never organized: pulling revision histories out of a control system, locating purchase files for modified equipment, having someone write an accurate technical description that a non-specialist reader can follow, and paying for a review that tests whether the claim survives contact with the legal standard. Where documentation turns out to be genuinely absent, the cost of creating a credible record going forward may be worth incurring before any petition is contemplated.