What's a 3sgte engine worth?

Broad question, without knowing what year/gen the engine is, what condition or mods, what's it comes with (half cut or ECU and wiring or gearbox lsd or non-lsd or driveshafts).

Whatever you look at keep lots of money spare to do all the maintenance before you put it in, these are 15 a 25 year old engines. Maintenance = almost a rebuild depending on what engine you get and want to do with it.

I have seen dud engines sell for under $1000, and others sell for $6000 (absolute bargain where they have put over $10k-$15k into the engine and haven't even installed it).

Basically dont rush into it, find out lots of details like has it been rebuilt / by who / when.  Find out what comes with it to ensure its compatible with what your planning.  
The cheapest I have seen over the past year is about $350 in basically buying a heap of metal and needing everything done to it, only the engine and nothing else.  The best value engines I have seen over the past year have been about $6000 with all the work and good parts done.
 
Whats your car currently? whats your end goals? and the members can try to guide you a bit further on what you need to look for and spend....

A standard running GEN2 goes for around $1000