Depending on where the blow is, it could be repairable.
If you're changing just the backboxes you can get a non-oem replacement from ebay for £250 but the quality will not be great - it could last 2 years or 10... Or you could get stainless steel backboxes for about £350.
Mine is now blowing by the middle box/ resonator (had it welded once but lasted a few weeks because the metal is so thin), so will have it replaced with an aftermarket one.
There are plenty of options to repair or replace, but depends on how much you want to spend on this.