I installed the DIY Rear Camber arms outlined in another thread on this forum. They work great and Pep Boys will do the adjustment once they are installed for about $50. The camber arms cost me less than $100 from Speedway Motors.
I also have an 04 that was wearing on the inside edge. I think this is from the shock or spring wearing over time. As this happens the rear tends to "squat" as if it was lowered and the natural result would be wearing of the tire on the inside edge.
If it is time, change the rear shocks to see if that helps being the rear back into proper camber before changing to an adjustable camber kit.
Just a thought.