Is your axle tag intact on the axle itself? Metal tag under a cover bolt.
Read it and use the sticky in the drivetrain section to decode the numbers to find out what you really have under there. Door codes are ambiguous or plain wrong sometimes.
When you say cheap, what do you mean? A really good LS costs nearly what a locker costs.
A "lunchbox" locker is like the PowerTrax Lockright (or their NoSlip locker), the Aussie Locker etc. It replaces the spider gears in your existing differential. It's a "streetable" automatic locker that most folks can install themselves. You don't need a micrometer and a precision low-range torque wrench to put it in. Just normal hand-tools.
On the street it is a little harder to drive. You have to be aware if you're going to apply lots of power in a turn -- but that's true of a limited slip also.
Junkyard limited slips are a bargain, but you generally need to rebuild them. Few folks actually do the clutch maintenance over time.
What kind of driving are you going to be doing, Tanner?