How much power do you want? Everyone is swapping to b-series, non-the-less they are great motors. Your d-series can handle boost. Calesta has some friends who are pushing 210-215 to the wheels with stock internals on a d-series motors. Upgraded internals and turbo cam and good tuning can get you 250 or so to the wheels.
For the money you spend on turboing the d-series, you could have dropped a b-series in, but if you are the type that is content with a certain amount of power, you dont like going faster and faster and dumping $$$ into a motor. Then pushing the stock (eh, i would upgrade for safety) d-series to 220-240 or so should completely satisfy your needs. You will be able to get a b-series and then do bolt ons for the prive of turboing the d-series. So..
b16sir 2 = 2250
b18c1 = 3200
b18c5 = 4650
b18b = 1200-1500
b20b/b20z = 750 (long block, no tranny)
Those are decent prices. Turbo kit for z6 is 2000 bucks and you will have more power and torque then anything listed there. (well, maybe more torque or the same torque as b20's)