When I have gotten offers of close to $300, yes that it is much of a lowball. I'm all for getting a deal, trust me. But I try not to go that low.
If you can get one for $200, this condition, shipped I wouldn't even be bothering with mine.

Take a look on Nasioc, my price is not out of line. The going rate is close to $300 plus shipping for a decent (not excellent) condition sti tmic with 20 - 30k on it.
$200 shipped for a vgc Sti intercooler is out of line (in a good way!) , and you should definitely jump on that other one.