If necessary, I have no objection to paying a special fee.

Literal

Necessary [conditional-であれば] special fee [object-を] paying thing [to-に] [regarding-対して] objection [object-を] state-not [polite-ません].

異議は申しません uses the humble 申す ('to say') with ません. に対して means 'regarding.' であれば is the formal conditional of the copula. Very formal/business register.