I e-mailed them back asking what the minimum for a deposit was, and was told that they accept any amount.
I'm honestly not sure if they even know what they accept.
If you use campbx, use delivery confirmation for sure-- or they will lose your money order and claim they've never lost a money order.
I used USPS for my money order and talked with the Postal Service agent at the register. He said that if they never cash the money order on the other side (gets lost in the mail, etc.), that I can return with the receipt and the money order stub and get my money back.
Also I think you can buy a money order on credit card? (I used cash). I might try this, and it might be dangerous.