I need some help deciding how to upgrade my axle.

I currently have the factory 28 spline 8.8" rear axle in my 99 2wd. I have a badly worn Auburn Limited Slip that I had installed back in 2003. The differential has 100K miles on it, it won't drive both tires anymore, and sometimes makes funny noises when the axle is under side load/off camber situations.

I need help deciding which path to take about replacing the differential.
Here's my criteria:
a) must be a LOCKER (I'm done with limited slip... 1.333 wheel drive ain't enough)
b) budget of $650 (I have a friend to do install for beer so no set-up fee)

I have the factory open differential somewhere in my garage, so lunchbox lockers are an option. Regardless of which locker I choose, I need a master install kit, right? Can I get a full carrier in there and stay within budget? If I'm limited to drop-in, which to you recommend?

I appreciate your replies.