first, be careful, water, paper and electricity are a dangerous combination.

that being said, if you have a local do it yourself moving company like
U-Haul, you can get something like this very cheaply.

...or you can find a furniture store nearby and find a refrigerator box,
or something else equally sturdy.

frankly, your best option would be to go to a Salvation Army store or
a used furniture store and pick up something like an old dresser or
and old cabinet, if you go lookin', you will find something suitable.

my own mother cab is just an old dresser i had and just converted and my
flower box is just a cab i picked up at the Salvation Army for $60.00 USD.

flower cab on the left, mother cab on the right.