How much you spend is dependent on the parts you buy, and how adventurous you are.
For example, you can modify the factory harness yourself. I've seen several successful examples of this, or you could buy a harness from S&P for about $1000.00 plus 250.00 to make a few adjustments. Or you could got the FAST or AEM route for 3K to 4K.
Exhaust, if you are willing to use Jeep exhaust manifolds and leave about 25 to 50 hp on the table you can do it pretty cheap. Or you can step up to TTIs and spend over 700.00
Motor Mounts, fabricate your own, or buy TTIs for 250.00, or go Alter-K for 4K.
Oil Pan, Pretty much plan on buying an oil pan, unless you've got some pretty good tig welding skills. They've come way down in price, Summit has the pan and pick up for under 300.00. Of course if you use an Alter K you can use a Truck Pan.
What I'd do is create a spread sheet and start pricing stuff out. If you found a low mileage 5.7 for 2500.00 you might be able to get it in the car for another $2500.00. The question you need to ask yourself, can I build a 400HP 360 with fuel injection for 5K?
Regards,
Joe Dokes