Seriously, though, you need to find an A&P with some sheet metal
skills. (Preferably a grand champion home builder, like mine, but
that's not really necessary to build a battery box.)

He could craft you a replacement part that would better than original
for far less than $700. And it would be perfectly legal.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993www.AlexisParkInn.com
"Your Aviation Destination"

Technically, an A&P cannot manufacture a replacement part such as an
entire battery box. He could "repair" the original box. The owner,
however, can manufacture a part for his airplane only and the A&P
could install it provided he vouches for its airworthiness. What is
meant by "manufacture" doesn't necessarily mean the owner has to
design and fabricate the part, but he has to be significantly involved
in some manner with its production whether that means supplying the
design to a fabrication shop or actually bending and riveting the
metal is not spelled out.