Why this route carries only one price
Some corridors carry two official charges, one at each end, and the second cannot be worked out from the first. This is not one of them. An apostille from United Kingdom to Turkey completes the paperwork in a single British stage, so the whole official cost is known before anything is posted, and working it out is arithmetic rather than estimation.
Turkey's position since 2004
Turkey joined the Hague Apostille Convention in 2004, and the certificate has been read there as proof of origin ever since. That arrangement is what removes the second stage and the second charge along with it. It also means the document leaves Britain finished, so every decision that affects the outcome is taken while the papers are still in your hands.
Counting before you post
The list comes first: exactly which documents the far end expects, named the way it named them. Leicester Registration Service at 115 Charles Street, Leicester LE1 1FZ issues certified copies of locally held civil records, one for each entry you need. The FCDO Legalisation Office at PO Box 6255, Milton Keynes MK10 1XX then certifies each of those sheets by post.
What each extra sheet costs
The published rate is £45 a document by standard post, or £40 a document next-day where the sender is a registered business. Multiply that by the length of the list and the official cost of the corridor is complete. Timing works the other way round: one envelope carrying six sheets moves as one, so extra documents cost money rather than days.
The decision that is genuinely yours
Nothing in this process asks how many papers to send, and nobody along the way proposes a number. The certifying office handles what it is given, and the receiving side abroad sees only what arrives. So the size of the bundle is a real decision, taken once, at the beginning, and it is the only variable on the route with a price attached to it.