Excluding my transmission, I estimate I'll be in my basic 5.7L swap for about $5,500-6,000. That's a rebuilt engine, cam, aftermarket ECU w/wiring, all new accessories, new radiator, fuel tank, fuel pump, motor mounts, oil pan, headers, throttle body, gaskets, spark plugs, etc. etc.
This is me doing all of the work and putting a number on taking an LA engine out and putting an, essentially, new 5.7L in the car on EFI. The transmission itself, bundled with all of the auto>manual parts is about $6,000 with a brand new Tremec T56 Magnum. But the post is talking about bare minimum for the engine swap, you can use a 904, 727, a833, etc, so that's not included.
Once you start talking 6.1L add about $3,000+
Once you talk OEM ECU, you'll need some other work there I don't want to deal with
New model automatic transmission? I have no idea on the cost there
And I'll add the current model Challenger transmission isn't very conducive to installing in our old cars, the shifter position isn't the greatest along with some other nuances.
Unfortunately there are a lot of vague posts on various forums that don't quite get the answers they need. Most of the time, the answer boils down to "it depends". I see posts like this quite a bit asking what's the bare minimum, then they go off on how they want a new engine, a 6.1L, upgrades, etc...quite missing the point. If you want the true bottom dollar, you're ready to wait for deals, you're okay with a used/good engine...I'd say about $4500-$5,000 will get you a running 5.7L w/EFI.
I get a lot of my swap information from a select couple of guys that have 6.1L engines in their cars. The info around this swap is extremely scattered. I recommend everyone interested to pursue swap information on the specific New-Hemi subforum at ForAbodiesOnly.com as well as the Facebook group "Gen 3 Hemi Swap". These two sources are the most densely populated with people dealing with this powertrain swap.