OR, you could egt the r33, and spend the 5 months saving up for $10K worth of mods in one go ----> definately equal a quick R33..
only about 4-5 years difference in make, and if you going to mod anyway like you were asking then your already on your way!!!
the S15 is basically the same as any SR20 powered car, which is then same as most import engines, mods wise!
but really depands on what you want the car for...
i believe that the R33 weighs more, but has more torque with the 2.5l, but the S15 weighs less with less torque from the 2.0l engine!!