I'm going to break ranks and take the opposite opinion on the peat moss. While peat moss may be better, it's not better enough to justify a 7X price difference. Coco coir is a serviceable alternative to peat moss. Coir often needs to have a calcium source added to counteract its high concentration of potassium. Toss in a generous amount of dolomitic lime (which will benefit the figs for almost all mixes), and you should have a workable potting mix.
Young fig trees are sensitive to having too much moisture. More mature trees are more tolerant of the potting mix and should be ok as long as the mix drains well enough to not be waterlogged. The proposed mix looks a little wet for young trees, but is probably fine for a more established tree in a fabric pot. Personally, I use a 5-1-1 mix (Pine bark-peat moss-perlite) for my young trees, and drop it to a 4-1-1 or 3-1-1 as they grow bigger. For a SIP, I alter the mix to a 2-1-1 ratio for better wicking. I substitute calcined clay oil adsorbent from the hardware store for perlite, and I imagine substituting coir for peat moss would also work.
The exact mix you use is dependent on your local climate, how mature your trees are, and how big a fabric pot you're using. I'm just going to guess and say that you could probably increase the composted pine bark content to 50% and still have a good balance of moisture retention and drainage.
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