I am almost finished a SR20DET conversion in my sunny sedan, the car is still a fair way off being finished but the conversion is nearly done.
Unless you are going to rebuild the motor with stronger internals, I would recomend starting off with a DET motor as they have stronger internals than the DE variant, which for a blown or turboed motor you would want.
A 2 litre turbo motor is legal in Queensland in a sunny but it would pay to check with the authorities down in Vic first.

As for blown or turboed, I would just get a DET motor and upgrade the turbo and do some head work myself, if, as you say you want to do some mods. But you could do some reserch on the blower that Aaron Fitzpatrick has on his SR in his 'FIVETEN' 1600.

Also, expect to pay from $1500 to $3000 for a silvia or 180sx front cut.