Don't know a lot about it, but my understanding is propane is about triple the cost of Natural Gas.
You obviously know you have to place the piping for this in the slab, so if you have poured the slab already it's too late unless you want to pour a topping slab.
These systems can be very nice in some aspects. Safe, quiet, don't blow the air around. OTOH, they don't filter the air and they are ponderous. They take a LONG time to heat up and cool down. Hours. So basically you have to leave them on all winter. You can't "knock the chill off", work for a few minutes and leave.
You also should install insulation under the slab and heavily around the perimeter, especially the edges.
I think the current technology uses high density PEX (polyethylene) pipe in the slab. Radiant slabs are rare here in the South.