Cheap bonsai soil

Should I use coco peat, perlite and lava rock as a cheap bonsai soil? 

Or is there a better alternative? 

Depends on what you are putting in it, if it is for finished trees then no, but for growing on apart from peat it will be ok. Akadama is by far the best soil for trees, with lava rock and pumice added. You only get what you pay for and skimping on soil quality will not be good for the trees.

I have another opinion than Geoff. It is based on my own experience, which I am certain Geoffs opinion is as well. I think the difference lays in climate. That Geoff do not have the constant freeze thaw cycles that we have all winter. Here the Akadama is totally broken down to fine dust in just one winter and totally useless in my opinion.

Locally we have several bonsai people that use 100% akadama as well. But they claim that very hardy trees will not survive our winters without frost free overwintering. It may or may not be a coincidence.

I have perlite and lavarock in all my mixes. Coco fibers I have not used in any mix, but bought quite a few trees in 100 % coco and it works as well. Not optimal, but acceptable in my conditions.

I think you can use that mix. Start with equal parts and adjust after your experience and personal preferenses going forward.

Thank you, that is great that I can use that mix. Bonsai soil is so expensive, but I will buy it in the future when my trees are older.

I use a hard baked clay used as absorber in workshops for my mixes. It has similar properties as akadama but lasts much longer and is durt cheap. That may be an option for your cheap mix.