Cable systems tend to be less expensive than mats because they take more on-site work. If you aren't paying labor, then that may save you some money doing it yourself. Check out
www.johnbridge.com for some ideas. INsluation on the floor helps, and under the slab even more (but that can't practically be retrofitted). If you have sufficient height, you can add some fairly thick insulation, bu tthat often means resetting or rebuilding the steps, or you create a trip hazard on that (first) last step. If you have a walk-out basement, that may also mean redoing the door(s). The only tileable insulating foam that can be used under tile I know of is Wedi. EasyMat has some insulating features, too, and it can be tiled on, too. If there are any moisture issues, I think Wedi would be better...not sure about moisture absorbtion with EasyMat (might be okay). Either of those can be purchased in various thicknesses, and the thicker, the more insulation (I think Wedi has more R/inch than EasyMat).