As mentioned it will depend on your rear diff as to what box to get...

Or if you want to spend some more and upgrade the rear diff too.

$1-2k to fix a 5 speed.
$1-2k to buy a 2nd hand box and smash it in.
$5-7k to fit a 6 speed. Upper end if you want DCCD or 06/07 spec.

Maybe need to factor $500 for a rear diff if the ratios do not suit.

Edit: What is actually wrong with your current gearbox? Personally I'd fill it with smurf snot and drive it till it breaks, unless you need reliability for track or something.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]