A QS will usually just measure through the openings. That means they count the same number of blocks for a blank wall as a wall with a window. They then price at €x labour and €y materials per block. This is because the reduction in the number of blocks and additional labour required for a window approximately cancel each other out.
To price the job yourself, calculate the number of blocks and ask a builders merchant the cost of the blocks. Maybe someone can tell you the current labour cost of laying a block. You will need to add about 10% for overheads and 5% profit. While that will not be 100% accurate, it will bring you a lot closer than the difference between €9.5k and €16.5k.
Maybe just go with the €9.5k, after all no matter what you calculate, you can still only get it at the price someone is willing to offer. Unless you do the work yourself.