I track prices on ebay off and on for 09 and up eagle headed 5.7's with and without the NAG1 trans, 6.1's, etc. If you find the right deal I think you can have a 09+ 5.7 and NAG1, with computers and wiring for $3-4k based on the asking prices on ebay. From there you have to do some cutting and then some work for wheel speed sensors with a tone ring on the back of the trans. 390hp/407tq and 5spd auto - it'll take a really healthy 360/727 to overcome that.
6.1/NAG1 with computers and wiring for $5k. I'm a little interested in the 6.1 because I want to turbo charge. If I wasn't I wouldn't look at the extra cost at all, just get an eagle 5.7

Watch the shipping charges and whether there are core charges, sellers are all over the place on those.