I've bought one, and plan to buy a couple more.
I just bought on eBay, paid with a Credit Card through PayPal. This gives me 3 separate avenues for accountability/charge dispute. Read the sellers feedback history, make sure they have a decent history, and have been selling engines for some time (I noticed at least one seller that had a decent rating, but almost exclusively on small parts...).
Best practice is to swap the intake manifold and all wiring over from the old engine.
The link that @idosubaruposted is for a bare, new shortblock. This will have a 1 year warranty.
Call your local dealership and ask about remanufactured shorblocks. These are about the same price, but come with oil pan, pump, water pump, thermostat, etc, and come with a 3 year 36k mile warranty.