This is my first post and I hope I have selected the right forum  for this topic....if not please advise where I should post. 
I am in the process of building a new house and have been thinking quite a bit about how I want to construct the basement floor.  The house is  a 2 story walkout and the less basement like I can make the lower floor the better in my opinion.  To start with I really dislike concrete floors in a living space.....I find them cold, hard and ugly and that's enough for me to seek an alternative.  So my plan has always been to create a wood floor environment without resorting to a poisonous p.t. foundation.  I'm planning for a radiant floor in this design so my approach is a little different than normal.  I was going to start with a V.B. under 4" of concrete than 2" of XPS foamboard with pex pipes layed on top between 1x6 boards glued directly to the foam board, topped off by a 3/4" finished wood floor.

I'm looking at a 1200 sq. ft. footprint and I estimate I'm going to end up spending $8-10,000 to pour that "never-to-be-seen" concrete layer.  I'm thinking that this probably isn't the best way to spend my money and thought perhaps I could replace the concrete layer with another material like well packed gravel, "roadbase" or even common sand and save around $8000.... if I do it myself.  In this case I would move the V.B. to the top of this alternate fill level directly below the 2" foam board.     I have searched the Web and have not been able to find any information or record of anyone creating a basement floor in this way so that has slowed my enthusiasm for this idea....a bit. 

Any thoughts or advice would be greatly appreciated.

Cheers!

Why reinvent the wheel? Once you put radiant in the slab, it's no longer "cold" and the "hard" and "ugly" can be taken care of with a floor covering suitable for use over radiant such as engineered wood flooring.

You'll find that a compacted-sand/concrete/XPS/wood sandwich is not appreciably softer than a concrete floor, with or without the concrete layer. There's simply no "give" to the system the way there is with joisted wood floors.

But the concrete lends long term integrity protection for the vapor barrier (ideally the bottom of your "all six sides of the cube" primary air barrier design) and keeps burrowing animals/insects from chewing in from below. Even if it's just a 2" non-structural rat-slab it's worth it.

But putting the XPS below the slab and running the tubing in a fully structural 4" slab adds significant thermal mass inside the thermal boundary of the building. It doesn't prohibit you from using a wooden finish-floor either, though a more thermally conductive finish floor would allow for cooler water temps for higher system efficiency.