I'd say the 4k number is probably pretty close. I was around $5k when I first was driving mine down the street, but I went the carb route, so the numbers were a little better initially. I've since swapped to fuel injection based on a good deal, but with all the options out there now you have quite a few different ways to go. If you have a decent setup already you can potentially get away with some stock parts, but everyone's situation is different. I used the radiator in my car just fine, but I've been told it was a C body radiator by someone at a car show. It's certainly bigger than normal, but it cools with zero problems, so you don't necessarily need a brand new aftermarket unit. Joe is pretty much on the money for prices though. Engine around $1500, fuel injection system around $1500, fuel system matters a lot of whether you go carb or injected. You can use factory manifolds, but headers make for a nice fit that's more or less "plug and play".
I originally looked at several builds for my car and kept coming up with a similar price no matter what I did. I looked at stroked small blocks, supercharged small blocks, aluminum big blocks, and gen 3 Hemis and all of there were coming in around that $5k minimum price tag. You can always scrounge up some good deals if you're patient and keep you eyes peeled though. It's also equally easy to spend money twice by not having a solid plan from the get go (ask me how I know...). The gen 3 Hemi has some pretty huge power potential without even needing too many aftermarket parts though, so that was a main selling point for me. Getting 400 hp out of one takes almost nothing, whereas building up an older 360 or something like that requires a lot of work and proper part selection and they just aren't as efficient.
