I've seen the 50% offer before to purchase Lightroom when also buy CS5 but here's a straight up offer:

$300 copy of Lightroom $150 instant rebate = $150 final cost

Here's the link to Adorama: http://www.adorama.com/ABLRV3MWE.html

It's a great price, don't delay if you've been thinking about upgrading to Lightroom from Elements or CS5!