I am hiring bulk sand and bulk terracotta suppliers, please PM me if you are interested. You could supply items to me once or a billion times. Also, keep in mind that since it is bulk that it should be less than market value.
Well one thing is that I think when buying in bulk the DC's should be cheaper because I am buying more. To answer your question I consider sand to be around 5k, I see multiple shops and people that sell it for around 5k and people who buy it for around 5k. If you think otherwise please tell me. For terracotta, I think its around 8k per dc. Please tell me if you think otherwise.