You're probably not going to find them below collector's prices at this point in time. With the recent DVD releases and comic books, it's more popular than ever right now. On the plus side, it MIGHT mean we'll se a re-release of some of the toys...
You should check out the official Voltron website (if you haven't already). Lots of cool stuff there. They just put out a Soundtrack CD featuring all of the original music!http://www.voltron.com
EDIT: Okay, looks like I was right - Toynami is putting out a set of all 5 lions, fully transformable, for only $59.99. That is an AWESOME price for a set like that, and well less than you'd likely pay for the old toys. There's info about it on the Voltron website.