You could follow the well published M5x route, M52B28 would deliver the best all round package for the money. Given that you're starting with a 316 you'll need to factor in suspension and brake upgrades if you want it to be safe & legal. Speak to Ray or Brent for a conversion package (engine, ecu, loom & trans), they'll be able to give you a realistic idea on pricing. You'll probably need a custom exhaust fabricated to suit, too.
If you used a conservative estimate of say, $2500 for a complete drivetrain package, $500 - $1000 for the exhaust fab, $xxxx for a reasonable suspension upgrade to match the increased weight in the engine bay, cert costs, bigger rubber and probably wheels to put your newfound power to the road, $300 - $1200 for the right diff.............................
Even with an M52, the cost could easily break 5 figures. If you were to use an S50B30 you can add at least another 4k to the 2.5k for the 2.8. 1UZ / M60 conversions would easily cost the same by the time the custom engineering is taken into account.
And if you plan to pay someone else to do the install it'll be exponentially more costly. I'm not trying to scare you off, but unless you can do nearly all the work yourself you could be better off looking around for a car thats had everything you want already done. For inspiration take a look at Hybrids "Operation : Weapons Grade". All 40+ pages of it, there's some really good info. Granted, his project is quite possibly one of the most comprehensively reworked E30s in NZ, but it'll give you a good idea of whats involved in doing a swap like this properly
Happy hunting!