All the shops around me are overly priced for their ski equipment so I was thinking of ordering online but I have no idea about the bindings/mounting business.

I am looking for a pair of twin tips in the $300 range.  Some options I liked were the Line Invaders and K2 Fugatives.  My ski style is mostly park.  Rails etc.  But I do like to bomb the hills and that too.

At this site http://www.untracked.com/ they have a free mounting service when you buy bindings and skis.  Does that sound like a good deal?  I could get a pair of Line Invader 07s for about $400ish
http://www.untracked.com/p1039c2b88-07_line_invader_twin_tip_park_freestyle_skis.html

What exactly do I need and where should I get it all is pretty much my question.