My 2003 Chevy Malibu is leaking water from the tail pipe and steam is coming out of the tail pipe. What could this mean?

It sounds like another blown head gasket or cracked block.

About how much does that cost to repair?

First get a compression check. Next determine what is broken. Third get an estimate from a shop in your area. --- It won't do you much good knowing how much they charge where I live.

If all the above checks out here is something else to check. Your muffler should have a small weep hole in the bottom of the outgoing exhaust end. It is there to let the normal condensation that builds up in your exhaust to get out but If it is stopped up it can only get out the tail pipe. Have only seen this once and it just happened to be on my own company truck. If no small hole is found there you can easily scratch around the bottom back rim of the muffler to free up the dirt that has it stopped up.

Pressure test the radiator/cooling system the results of this will eliminate and or confirm a couple of possibilities. More than likely your going to have to have your worped head machined flat probably like what should have had done first time round.