If you're looking for something from a crate, then there are a few areas to be careful of. Most of the GMPP crate engines are not set up for truck use; they've got a cam for making HP up high and not torque down low. A 383 is by far the best bet for a SBC truck engine - 50+ more ft-lbs of torque, and it should not be "quite a bit more" expensive; the GMPP 383 has a forged crank and internals which is why it seems to be so expensive. A decent 383 should deliver 400+ ft-lbs through 4000 RPM and cost ~$500 - $750 more, max.
400's do have some unique quirks for the extra displacement. Realistically these are pretty scarce any more used, and the crate engines typically use new aftermarket blocks...so are quite expensive.
I'm not a big fan of crate engines, so I can't give you a bunch of pointers. I have had some good luck with shortblocks from Golen Engine Service (
www.golenengineservice.com) and they can build you a decent cast 383 for a very nice price.