I just checked the B & H website. They sell the same combo for $599.99 with free shipping in the US. There's no mention of any rebate.
Its a little bit more, but many people consider B & H to be the gold standard for online camera retailers.
On Resellerratings.com, Butterfly has a six month rating of 6.27 (out of 10), definitely mediocre. B & H's rating is 9.71.
BTW, the Pentax USA website (
http://www.pentaximaging.com) says that there are no special offers currently being offered, so where is that other $20 coming from?