Invictus, a couple things....
To start with Columbian rainbows,E c. maurus, don't require the extreme high humidity that Brazilians do. They are commonly kept on dry substrate with a large water bowl, similar to common boas.
For Brazilians, Bloods, and Anacondas I have used
ordinary cheaper than dirt "PEAT MOSS"...
It is simply Spaghnum, processed and ground up . It's fairly sterile and is compressed into large bags. Its dry when you get it, so there isn't much living in it.
You can get huge bags, from Canadian Tire, Walmart, or Garden Centres for only a few bucks.
Yes , the plant by nature is acidic, and that is why you want to use it, because the low pH inhibits mould and bacterial growth... You wont get any fuzzy stuff growing on peat!!
The only draw back is that you must keep it moist, because it is very dusty in the dry powder form.
I used to simply pour a small bucket of water in the cage when the substrate starts to get dried looking.
The snakes pat it down into a pretty solid mass, so the dust issue isn't critical unless you're removing the substrate or putting new in. The dust isn't toxic or anything, but it can clog nostrils, and make the keeper sneeze.
This substrate is also safe to feed on, and thats another big plus.
I've lost snakes on cyress mulch do to ingestion of the long sharp toopick like bits that come in it... So if you use Cypress, you better feed somewhere else, and as your collection grows, you'll find that a big pain in the butt... at least I did! I feed everything in the cage that houses it.. No time for musical chairs
Give Peat a try.... its dirt cheap,,, no actually its cheaper than potting soil.
Jeff has a good point though... Paper is free
I currently keep only dry species and have them all on Alpha or Beta chip made by Nepco . Not sure if you have a supplier out your way, but these are lab grade particulate substrates.
They can be spot cleaned, and I also feed on them..everything except small newborns...