Supercharging easily yields 400+whp but you will need to upgrade numerous things along with it...
First, supercharging systems
Active Autowerke VF Engineering ESS Tuning Dinan
These are a few of the numerous supercharger systems available out there for the S54.
You will also want to upgrade the following pieces as well in order to bring reliability to the E46 platform as well as stiffen everything up over stock.
Rear subframe reinforcement
Heavy duty transmission mounts
Rear camber arms - OE are known to bend on high horsepower M3's
Exhaust - for maximum flow but not 100% necessary
Suspension - once again not 100% necesary but upgraded suspensions on supercharged M3's help put power down (particularly in the rear)
Brakes - factory brakes are good, but with 400+whp you're going to want to stop faster
Wider wheels - factory 18x8's with 255 tires are not enough to put the power down. Not 100% necessary but definitely helpful
The list goes on and on but I've hit the major parts.
The total cost on all of this is going to vary, but with most supercharger systems going for $7K+ expect to shell out BIG $$$$