So whats this kind of swap cost to do???

Alot of people are staying away from the 6.1 due to the altenater being down low it requires frame work for clearance. Depending on how low you want to go a used 5.7 can be had for a little as 1k. But keep in mind this will be a used one probably requiring a rebiuld. I have seen people geting rid of crate 5.7L set-ups for a little as 6.5k. This being with the harness for plug and play.