$3000 for the RB25DET (just jap)
$1195 for the RB20DET
You'll need a stronger gearbox (RB25) which is about $1000. Optional but recommended to replace the front brakes with R33 brakes as they're slightly bigger (and better).
It'd be cheaper to buy a R33 front cut. Atleast that way you'd have some extra stuff to sell like the headlights and quarter panels. I'm not too sure how much they are as I can't find a price anywhere on the net (not really trying).
Labour? a few slabs if you do it with your mates, you'll learn a lot from it as well.
If you're going to get a mechanic to do it, might cost about $1000 if nothing goes wrong...