While the SR20DET is a popular motor, I personally think it is over-rated. It is a VERY heavy engine. All said and done it is twice what our motor weghs. An LS series v8 weighs less than it does.
If you are going to swap it with another motor there are many other, better alternatives. Sr20DET is fine for Nissans, but if you are changing it from a BMW motor why not do it with something cheaper to build, maintain, and easier/cheaper to acquire. Look into GM Ecotech, Ford Duratech (Focus motor), Buick/Pontiac 3800. GM has a guide documenting exactly how to reach any power level you want from the Ecotech up to 1000hp and more. The Duratech has lots written and available by way of Focus parts. 3800? Look into a Bonneville or Grand Prix. For ideas, check out some Grand Nationals (streetable 600whp, oh yeah!), some even have factory superchargers (300hp), use an S10 trans, and a T5 or T10, good to go.
These motors, barring the supercharged versions can be had CHEAP at a salvage yard on bargain days. I can get most of those for about $60 on those days. $40 more for the trans. The GM's also have a bonus, a great injection system that a cheap connector will allow you to hook in a laptop and tune and the Ford computer is self learning.
Will your car be as original, no, but when you are flying down the road, who cares. By the way, a non-supercharged 3800, should get you between 30 and 40mpg, even with 240hp and only adds about 35 pounds to the car.
Unless it is one of the ones listed, expect to spend several grand on the swap alone. Even with a GM, it can run into the thousands if you are not careful. For the price of an SR20DET conversion, you could easily get Downing Atlanta Supercharger kit or a bit more a Metric Mechanic motor. And that is without mods.