I get about 3 by 3 cubic foot bags of cypress mulch for 5$ from Taylor do it yourself center in Va. But you could get it from any hardware store or gardening store they have in your area I suspect. It's a little "chunky" but it holds humidity better than anything else I have used and is super cheap.
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I am here: http://maps.google.com/maps?ll=36.942417,-76.295445
1.0 normal bp- Blitz
1.0 Nicaraguan boa- Gavin
0.1 Red Tail Boa- Tara