When it comes to soil I use pretty much the same thing most the guys in my local bonsai club use which is a mix of pine bark soil conditioner, Napa floor dry (bag #8822) and then a bit of top soil. I use about 1/3 of each amount in my mix.
The pine bark soil conditioner is nice and loomy so drains quickly, the Napa floor dry #8822 is to help drain quickly (it works just like pumice but MUCH cheaper) Just be sure to get the Napa #8822 because it does not turn to mush like other brands will. And the the top soil is just to retain some water because I am gone on fishing trips so much my trees sometimes go 3-4 days between watering, but most guys forgo the top soil and just use 1/2 soil conditioner and 1/2 Napa floor dry.
Much cheaper than buying the premade 1 gal bags for $5. I use to but the premade stuff when I first started but now make all my own with the above mentioned stuff. I can usually make up about 40 gal or more out of about $10 worth of ingredients.