ARP headstuds and a new headgasket would be minimum requirement for me for reliability on the k04 engine.
Been looking into this alot recently and i reckon your looking at £4k easily for the turbo, RS4 injectors, modified intake, in tank fuel pump, ARP head studs plus headgasket, new map not sure how much Revo will want over 2+ and then theres labour on top.
I guess you gotta pay to play.