Order is what this route costs you
Most of the money lost on this corridor is not lost to fees. It goes on stages done in the wrong order and paid for twice. Gabon has not joined the Hague Apostille Convention, so a file passes through more than one pair of hands, and each pair expects the previous mark to be there already. Get the sequence right and the fees are simply the fees.
Stage one: the copy that travels
Nothing begins until there is a signed paper somebody is willing to let go of. Edinburgh Registration Service at City Chambers, 253 High Street, Edinburgh EH1 1YP, prints certified extracts of Scottish civil records, and a fresh extract is a signed record in its own right. Let that extract make the journey so the paper you cannot replace stays with you.
Stage two: the British mark
The FCDO Legalisation Office is the United Kingdom's authority for apostilles. It works by post from a box in Milton Keynes and keeps no public counter, so this stage is an envelope out and an envelope back rather than a visit. The charge is £45 for each paper, or £40 for each paper on the faster route open to registered businesses.
Stage three: the desk that finishes it
The last stage is the one that makes a Scottish paper readable in Libreville. An official acting for Gabon looks at the British mark and adds one of their own. This is a separate act, by separate people, with its own charge and its own queue, and it cannot be started while the British envelope is still somewhere in the post.
French, and where to put your slack
French runs official life in Gabon, so an English extract commonly travels with a French version beside it. Getting that done during the British stage, while an envelope is out anyway, costs you nothing in time. Put the spare weeks at the consular end instead, because that is the one stage whose pace you cannot influence at all.