Hi, I'm building a brand new bathroom and laundry in a new site. there is nothing there now besides the walls and pipes. I got a couple of quotes and they said $900 for the laundry and bathroom. Including the waterproofing certificate for the certifier. My tradie recommended me a new waterproofer that quoted me $500 for the same including the certificates. Is that suspiciously cheap or it sounds reasonable? Note that bathroom and laundry are on a concrete slab on the ground floor so no risk to leak underneath. Thanks!