It depends on how much boost you are going to put into it.
Compression is real high, close to 11.1 in the ls2.

The Alum. block are not all that stroung alot of guys like the ls truck blocks b/c they are strouger "iron"

If you are going to make a lot of power you are going to need an LSX block or at least change the pistons out for lower compression ones.

Plus the price of the computer and wiring for the engine.

Cost on either motor will be close to the same as both will need alot of non-stock parts depending on the build you want.

What ever you decided it is your car have fun with it.