The contractor quoted me that figure to go down to the drywall, take it out, place waterproof membrane, new tiles, and tub and paint the bathroom.

So far I can only find roofers who will be membrane roof ($16,000) with a 20 year warranty. 

As a roofing estimator I highly recommend PVC membrane. 

If you can't do much to change the grade, you can install a Geotextile membrane around the perimeter.You don't want to put this all back together until it's right or else you will haven this problem again and again.

You can get a roll on crack-supression/waterproofing membrane if the slab has issues.  

You will also want to have the flexible shower membrane behind the bench, extending a foot beyond the bench.

@Gregg Reinbold I think using an uncoupling membrane such as Ditra, will help reduce sound transmission (http://www.schluter.com/6_1_ditra_6552.aspx).  

Provide an area floor drain near the WD and water proof membranes in all wet spaces.The toilets waste should be a 4" diameter, so you can save a few bucks here and there.

Mount the hoses high up and secure about 2 to 3 feet from the nasal so when water is on it swings around, up and down shooting water out.

., another suggestion: Home Depot has Home Decorators bamboo by the pallet: it is a nice color (not too dark not too light), not really out-gassing, it is a 2-2.5 on the 1-5 hardness scale, it does not split that easy and is not involved in the formaldehyde lawsuits that lumberliquidators had for the similar bamboo...price is between hardwood and laminate.i'm on the first floor and i got this sandwich: concrete floor, 2x paint membrane, glued 6 mm cork, 3/4" plywood screwed into concrete, tar paper, bamboo on top nailed in.