not sure about a stock k-frame car. but in my dart a LS motor would be probably half the price.
can get an alumn LS with OD trans for around $3K. just have to get the proper mounts (and weld on brackets) from rms to be able to bolt the LS on to my alter-k. a $400 set of camaro headers will fit with the alter-k instead of a $1000 set of tti headers. computer set is about $1800 and i know a guy that will plug a tune into it.. up to this point yes its about 6-700 dollars cheaper for the LS. where the big money is saved is the OD trans i got with the motor. in a mopar you are looking at $3K on top of the engine swap to do a OD trans..
the after market for a LS motor is just an added bonus...