That is an OP sketch, yep. I've seen cels from 
the sequence go anywhere from $350-600 range. As 
for what the sketch without the cel would go 
for ... not really sure. Most I've ever paid for 
a garden variety (non-OP) Weiss sketch was in the 
$15-20 range and I'm not sure I'd pay much more 
for just an OP sketch, given the availability of 
actual cels out there.

Sorry I can't be of more help.