Hmmm. Figure $35-40/day for rentals on something really decent, demo-quality that is. Say you ski for 6 days, that comes to $240 or so, poss. less.
You -might- be able to score a Volant Chubb or 1080 or Volant FB or K2 PE or Volkl V-Pro/Dogen/AX4 or older Rossi B2/XX for less than that but not much less. And you're buying a pig in a poke.
Now you say "Many times when I ski powder here in the east, my boot comes loose."
a) Check that your bindings and boots are clear of snow when you click in. One little teensy wedge of compressed whitestuff can play havoc with release settings.
b) This can happen when the skier tries to muscle a tip-diving ski into the same turn behavior he might see on hardpack. The stereotype for this would be the top-to-bottom jump turner.
Powder skiing is much more relaxed than this. Check some of Crush's threads on this board.
(PS disregard non-Tahoe powder ski reviews. Tahoe snow is MUCH different from Utah snow).