No escape from the dollar sign in SED

I was reading the excellent SED FAQ bud could not find an alternate solution to the following: 
 
The script below replaces the literal string $path with the contents of variable $usb 
 
The only way I could get this to work under busybox ash is with completely bare \\$ 
to escape the literal $path in two separate chunks as \\$'path' which is REALLY weird. 
 
root@zero:~# usb='/mnt/stick'; echo 'Path $path is it!' | sed -r 's|'\\$'path'"|$usb|g" 
Path /mnt/stick is it! 
 
It's great that it works because it allows me to pre-process my here-block before I 
write it out to a file, but jeepers it would be nice to understand what's happening 
and whether there are any other ways to do this under busybox with ash. 
 
Here is the slightly simplified here-doc version which I actually use: 
 
usb='/mnt/stick' 
cat <<-'EOF' | sed -r 's|'\\$"path|$usb|g" 
echo and here it is: 
ftpdir=$path 
echo more stuff 
EOF 
 
Best regards 
Stepan Novotny 
 
 



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