This has to be the no1 most common failure on a zed, especially on cars over 4 yrs old.
1; NEVER buy an exhaust from the stealers. Forget kwik fit and the like, as they don't do exhausts for the Z.
2; If moneys tight then see if it can be welded, or look for a 2nd hand box on here or ebay etc, around £30 to £100.
3; Buy a stainless steel system from one of the many traders on here, prices ranging from £300 to how deep are your pockets