putting a ford 5.0 in a 72 Dart
LS swap aren't they dime a dozen cheap like 318s used to be?
LS stuff is cheap, but not like SB mopar used parts cheap.
the manifold you'd want to use (LS1/6) with fuel rails and injectors run about 4~600 give or take, LS carb ones are 200+ (unless you want hong kong phooey ones), but then add a carb to that. then the real fun begins with the wiring and PCM and flash tunes. and that's supposing you have the correct accessory drive for what you're trying to accomplish. you don't? cough up another 1200.
you could probably do a dirty LS swap for a few G's less if you were thrifty, shopped smart, bought used and had time to accumulate everything-- and had some skills-- but also didn't care if it was neat and tidy and done well.
the same goes for G3 swap. i did some back of the napkin math on it about 2yrs ago and if you just put everything in the cart and wanted to melt a credit card buying all new it'd be about 12K with a full half of that being the motor.
like for like though, doing a swap with either using top quality components the price difference is surprisingly close.