Yea it is a lot of money to put in an old truck, but I have done it,...twice,..and love the trucks that I have ended up with, and have no regreats. It only makes sense to do it on a good solid rust free truck that you plan on using for years, and is a good truck allready, IE, brakes, suspension, tires, accessories etc.
The price of the swap depends largely on what your skills are, and now patient you are. But for the most part $5K is a pretty bare minimum for a swap including a motor. I don't know about the wiring on a Common Rail, but any early VE pump, P Pump motors, the wiring is very easy, No computer to mess with, and will run with 12v to the pump just like an IDI.
Quick break down'
$2000.00 motor if you can find one for that price, I have seem some VE pump motors for around $1500.00 lateley.
$800.00 Adapter Plate
$350.00 motor mounts.
$350.00 intercooler boots and custom piping.
$350.00 Moving the trans and transfer case back, and changing drive shaft lengths.
$300.00 misc gaskets because you will end up regasketing the motor, taking care of the KDP while you have it out.
$300.00 Misc, hoses, power steering, air conditioning,
$200.00 Misc brackets for alt, ac, vacuum pump.
$300.00 Hydtoboost if you don't run a vacuum pump
$4950.00 total just off the top of my head, Some numbers may be high, but all are close to reality. That is not taking into account any other incidentals that you will run into, Exhaust, Pump upgrades, Injector upgrades, bad turbo, New Clutch while it is out, adapters for any gauges, air cleaner, cables,...etc ...etc,..etc,..
You get the idea, figure $5000.00 and double it, and if you do it for $6000.00 you did great!
That said, where the patient comes in is on the front of the project, waiting for the right deal to come along when you buy the motor. I was able to buy a 1985 Ford F350 that had a 20K mile Cummins Swap already done to it. Most of the basic that I need for my swap came with the doner truck.