How much to weld torque boxes?

I have not gotten anywhere with ford on getting my car fixed so I think I will just get it fixed on my own. The right side torque box is busted, but how much does it cost should it cost to get it fixed and the left side welded up as well? Ford quoted $1300 to fix it and that is too much. Also what all is involved? Do they just need to unbolt the control arms or does the whole axle need to be dropped and realigned.

Are there any parts in my sig, minus the prochamber it has been removed, that Ford could say caused the torque box to rip apart? They blamed it on rough driving and my pullies.

I have no idea how it happened. I have the original factory goodyears on the car and it only has 28,000 miles on it. I do not drag race, street race, or drive any harder than the average Mustang GT driver. I think that there was a defect in the welds on one section and it broke loose and eventually the other parts broke loose or cracked. My car handles like crap now and I can feel the rear end move everytime I change gears.