Is it cheap if i'm quoted RM450 to do retile for a toilet measuring 40sqrft (4.5x7.5 ft) with tiles included?
No hacking and removal of tiles, just scratch and lay on top of existing tiles

No water proofing,, is it necessary?

1 bag of sika top seal 107 + 4L liquid polymer cost only 90++ @ hardware shop, more than enough for 2 coats to normal size bath room floor and shower area wall.

so, u know how much more u need to pay your contractor  

you need at least 50K for it...