ive been poking about under the mini and ive found rust hole underneath the crossmember on the floor pan. well pi##ed off as its just come out the bodyshop, they put new sills on, how didnt they notice!!!

but anyway, i was planning on doing it myself as i know it will be properly then.
so the questions are-
when i put a new plate in, is it worthwhile replacing the crossmember? as i cant see how bad the metal is underneath it?
is it an easy job? i take it, its literally just cutting it out, and welding in a new one?
how much? i cant find a price on the web..
the crossmember has been patched up loads before and i think it would look a lot neater, but im scared in case i find more nasties lurking underneath it. hopefully ill find an old 50p?

thanks in anticipation