I thought I'd do an open letter about this since others might be
considering it also.  There are several sites on the Web that show you
how to make a ferret cage out of those wire panel things they sell for
storage usage in places like Bed Bath and Beyond.
 
http://www.bedbathandbeyond.com/product.asp?order_num=-1&SKU=13652600
[corrected]
 
They are held together with plastic corners so it can be made into any
configuration you chose.  You would need to add your own solid floor,
however.  My husband and I have seen some amazing multi-floor cages made
from these and they are relatively cheap to make.  We got some in order
to make a "time out" cage for a new big bully ferret while he learning to
play gently with our little girl fuzzies.  There was one big problem with
those panels we discovered.  The spaces are fine for holding in our big
boys but about half our little girls are small enough that they can go
right thru the squares.
 
If you use these panels to make a cage you need to make sure your ferrets
can't fit thru the spaces first.
 
Nancy
[Posted in FML issue 5181]