Welcome to Android Central! You can bet on it. Hard to know when, though. You could try asking your local wireless rep really nicely if he or she could give you an idea of any upcoming price cuts or sales.
It's currently showing 299$ through the pre-paid phones page. Not sure if it'll work on post-paid plan, but I don't see why not?? Asked a rep online, and they said no.... but maybe someone smarter than me can chime in.... I was thinking of doing a similar thing, hoping it would drop in price once the G3 got here. And for half the price of the G3, you can't really complain!!
EDIT: Prepaid verizon phones need to be active on prepaid for 6 months before they can be moved over to contract plan. Disregard my excitement/previous statement. I hope it goes down to 400$ soon off contract, but it's looking like it will just be free with an upgrade :\