Yep, just like Mars 302 says, they really don't have problems anymore. A 347 is a good choice if you plan to stay naturally aspirated. A lower compression 331 (8.5/1) is real nice if your future plans include a blower or turbo.

Here is an example - 331 w/ forged pistons, crank, rods - $2000. That will include your machine work, gaskets, bolts, etc. It gets a little more expensive if you add a windage tray and main support - around another $300.

GT40 steel heads - $400
E cam - $100
Kenne Bell blower $3000.
450 RWHP - Priceless.

Edit - I know this isn't a $1000 shortblock. It's real easy spending other people's money.

Anyway, look at www.jdsperformance.com

He is a real good guy with a shop in Orlando. You can pick up a balanced 331 or 347 (they are usually the same $) with good quality pieces (not all forged, but high nodular steel crank, stainless rods, forged pistons) for about $1100.

Again, think about your future needs. Some aluminum heads require special pistons. You want low compression is adding boost later.

A nice 331 making 9.5/1 compression with a nice cam, aluminum heads, and intake should make 350 hp.