Relux Slabs

I was told a "waffle" slab would be much cheaper than a regular house slab. I approached Relux for a quote and they gave me a rough estimate over the phone which was about half the ptice of the estimates I had for a regular slab. Relux told me that I would need to spend about $300.00 having a special engineer design a waffle slab for me and then Relux could give me a written quote. I spent the $300.00 on the engineer they recommended, then I got the quote and it was more than double the original phone estimate they gave me, and in fact, exactly the same price as a regular slab! Not happy with Relux since I wasted $300.00 and for this reason I went and paid for a regular slab...why buy a waffle slab when I can pay the same price and buy a normal slab which has twice the concrete!