if your car has bent chassis, it's considered a write off, so probably not worth repairing.
first thing first, where did you take you car for a quotation, HK island or Kowloon or NT, as you can cheap and decent repairs in NT, but some are dodgy, some are decent and trustworthy
why are you not claiming off the perpetrator's insurance for this accident, are you in the wrong or more likely, the driver behind you?
I presume your car value is slightly more than the cost of repair, hence, why you are asking, have you consider taking to other garages for a quotation?