A genuine SE K750i housing is around R100 trade plus a keypad at around R30. There (as I recall) a couple bits that you do not get, although listed as a complete housing! I think one is the memory card cover. Not sure if my supplier still has them? I only have the face in stock. If you can find a genuine independent dealer the job shouldn't cost more than R250 or R300 with a new generic battery thrown in!
Don't be tempted to get a generic cover fitted, to give you a clue of the level of quality they are R8 plus VAT trade. I only order these in for the battery cover and then dump the rest in the bin. Even the R15 kids toy phones will look like a N95 compared to a K850i with one of these generic covers fitted! Plus you'll lose a friend for sure!