Just beware, JDM engines usually aren't in the best of condition. A complete rebuild is usually not needed but it will most likely require some work. USDM engines are usually more expensive and may or may not be in any better condition then their JDM counterparts.
The problem is really that most 300ZXs are either over or approaching 10 years old, making replacement engines in good condition a rare find.
Example: My own JDM replacement, it had a legit 20,000 miles on it, was out of an automatic TT that must have really been babied. Inside and out every moving part was clean as factory fresh, save for a bit of rust on the various gears in the front (which is where the 10 year thing comes in, the engine must have sat outside somewhere for a while). Even in such great condition, I'm replacing all of the stiff old PVC and IACC hoses, the IACC valve and a few other things. There is one or two other items I would have to replace/fix but I'm upgrading those so no worries
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Now, Broke being who he is, I would suggest you take the time to do any upgrades you plan on doing while the engine is out. For example, it would probably be a sound idea to replace the seals around the turbos. Now dropping $1500 for some new JWT 500s might be a bit of a stretch but getting a $400 set of ported exhaust manifolds is a pretty good upgrade for the cash. Anyway, just something to think about.