AOC Costs...
The costs most definitely will vary depending on how one develops their Operations Manuals. My experience has shown that operators wishing to 'do it themselves', end up spending more money than if they'd contracted the services of someone who knows how to write the books.
There are many who profess to know what/how to write them but I've read and rejected a lot of garbage.
Spend the extra and get a professional to get the work done. AND..don't buy the aircraft until the approval signatures are about to be placed on the first page of the OM.....and..the costs, depending on the complexity of the operation can run upward to 500K to 750K.