I am looking for a roundtrip airline ticket from Portland to Las Vegas for under
$150.00 from Friday March, 11th to Sunday March 13th.

I checked with mobissimo.com  and the cheapest they are coming up with
is $374.00 with America West. When I checked on America West's own web
site they came up with a fare of $344. I doubt if you will get
anything cheaper for the from and to destinations and dates you
mentioned. (If you are flexible on the dates you may come up with
something cheaper) You could also call America West as they appear to
be the chaepest airline for this route.
Cheers
Mongolia

HI, I checked somewhere and got those prices too, but now I  s e e m 
to recall that the casino hotels in Vegas offer flight-hotel packages
with discounts on the flights if you stay in the hotel, speculating
that you'll more than make up the difference at the tables.
But I don't know if this is true, but could be another approach, for
you or a researcher.