Where are you based?
Are the backer boards needed?
Do you really think topps is the right place to buy material's ,the only thing i buy off them is sponges.
You have to look at it from the client's point of view, they see an area and expect it done for button's instead of giving them a flat rate for the job ,break it down into what is needed i.e underfloor heating alone is going to cost X amount ,backer board's X amount and tiling X amount i think your rate for travertine is there or there about's.
Breakdown the charge's for them and let them decide if they need the added extra's of underfloor heating(sound,s very expensive at £610 as you dont need to cover the whole £23m2 ).
Hope this helps
