first off welcome to the board. Its good you are hear at an early age.
About the SCC I think eveyone on this board has read it by now. It is possible to get an SR in an S13 for 3K but VERY hard. First you have to find a car (preferably w/ a blow motor for cheap price). then ou have to find a front clip for cheap, and you have to do all the labor by yourslef (with a few friends). Don't get your hopes to high, getting an SR powerd S13 will range from 3K-7K.
Before you purchase your car find out as much as possible about the car etc.
Here are a few links for help:
240sx.org
Unstable Hybrids
SR Swap