That would be something I'd be up for trying...if
I can find a chunk
of core of low enough density to trace the wiring in. There are some
nice low-density planes on eBay right now, but they are priced WAY too
high in my opinion.
$35 is a good number to stick by. The MIT swap meet semiregularly
offers various types at that number. A real small low dens one might
be better at $20 but even those often sit at 35.
eBay looks to me like $35 +- $15 most of the time.
John A.