If it helps any other than the title and the minion for completing turn 13, there are really no benefits to getting past turn 9, as pretty much everything from Turn 9 is mostly obsolete and can be surpassed with casual gear or crafted gear.

Coils completion is not required for any of the 3.0 Heavensward content according to SE. So it really is not required.

That being said while I find the price for coils carries it is not an unreasonable request.

You are asking 7 other people that don't know you, are not in your FC, or have any affiliation with you to take the time out of your day to carry you through content (meaning they are already playing 1 player down from the start. They also run the risk of actions you take causing a loss. To top it off each of them have to split the funds 7 ways.
They went through and on their own completed the content, and mastered it well enough to carry someone else with them. So a gil for carry request is not unreasonable.

As far as the cost they technically have the right to charge whatever gil they want. If people are willing to pay it then that kind of helps set the price. Is there a reason you can think of that they should offer a lower price for you, that does not apply to anyone else?

If you are wanting to complete coils, and your group is not working out, it may be time to seek out another static to work with and learn the content. From there if you want you are welcome to work with your group and see if they can carry the others. It happens. That is honestly the best way to get it no charge or low cost.

As far as the gil itself, If you have crafting and gathering and you put your time to it, you can pretty easily make that kind of gil, in a reasonable time, especially if you unlock the Masterbook 2.

If you don't do crafting, gather, or other content, I don't know what more I can recommend.