Id be pulling apart the old motor to determine what exaclty went wrong first. If it was a blown head gasket it wont mean a corroded head guaranteed.
In a bi metal engine when it overheats the head and block will change their temps causing the seal the head gasket has to break, causing the blow.
People say u need to reskim the head as it will have warped when it overheated, and that the head needs to be tested for corrosion. I dont believe in doing all that if u can see it looks ok, and test for straightness on the mating surface. (im a dodgy bastard, but it saves heaps of money.) *insert flaming "oh noes its gunna blow again, u need to do it right" replies quotes below Do all the labour yourself and u should come out of it very cheaply.
Rb30det would cost as much as the 25det route, dont even consider the 30e. 30det can be done on a budget as well, no need to go uber the top.
But sort out what went wrong first, before slapping in a new motor. Plenty of guys in SA have done the 30det (including the 4wd), so ask and u will receive help.