Prices for RACP reinforcement can vary greatly... the number of cracks to fix, whether the left rear seam in the wheel well has split and needs welding, are you going to replace your bushings or not (and which bushings?) all influence the cost. Best thing is to call a few reputable shops and ask for quotes.

Mine was ~$1800-1900 CAD to fix all the cracks, weld the split left rear seam in the wheel well, weld Redish reinforcement plates, paint/undercoat the affected areas. Then install powerflex subframe bushings & RTABs, and OE diff bushings. Keep in mind this was 5 years ago, that shop had a great deal and prices have likely gone up since.