A $50 bill will convince many stone shops to run they on their saw.  All 4 sides can be squared in about 30 minutes.  The edge will not be polished, but will be square. 
There are now a lot of bottomfeeders in the stone countertop industry.  I looked at a Chinese import Granite slab yesterday, 8' long, polished on the top and two sides for $79.  The slab you have is thicker (much better) but it is hard to beat the prices that are showing up. 
Aaron