Coco and Potting mix for guerilla?

Hey guys I'm planning my first grow and i intend to veg indoors and flower outdoors. I live in australia and im finding it impossible to find good value perlite. I was thinking of mixing searles premium potting mix with coco coir. the coco coir description states it is "an open medium with excellent drainage". The potting mix has alot of organic matter and fertiliser as well as water crystals but I'm worried about aeration and drainage. Will coco be a suitable substitute for perlite when mixed with potting mix? I'm planning to use a lesser ratio of coco as I dont intend to visit the site more than once a week. ive read other threads saying that the presence coco will require more watering but would the increasing rainfall and water crystals counter this? my main concerns are aeration, drainage and watering frequency. so would a coco/potting mix combination be appropriate for an outdoor guerilla grow in my circumstances? sorry for my lack of knowledge, still doing lots of research for my first grow. any advice is appreciated thanks guys.

Rice hulls make a good substitute for perlite.