How much do you know about the subaru motors?
You can get a new EJ25 block for like $1,600 no internals.
If you know how to build motors I'd say buy a new block, buy the STi Crank for I believe around $370.00. Forged Pistons for like $867.00 another $1,000 for some Forged Rods. About $90.00 for Rod Bearings about $128.00 for Piston Rings about $12.00 for Pin Clips. You could have yourself a Built Short Block for around $4,000-$5,000 if you know how to assemble a Subaru Short Block.