I am wondering that if the housing's inside surface was scratched and damaged by the rotors, can the housing be rebuilted or reconditioned? or need to buy a new one?

 

Some wear along the outside edges is normal, but if there are any gouges or deep scratches you'll need to buy new. Generally speaking if you can feel your fingernail catch on a groove its toast.
Have them inspected by a qualified rotary specialist. They cannot be resurfaced.

 

So, do you know how much for a housing?

 

Oh, about $550.00 each. If only one is damaged it's a good idea to replace both - that way your compression numbers should be about the same. Of course you'll need new apex seals and a few million other tiny parts, seals, springs etc. that are outrageously expensive. It's basically going to cost an arm and a leg - maybe both legs!:p Good luck!

 

Consider a reman or a j-spec for the price that its gonna cost you for new housings, seals, springs etc etc....