That could be a hard question to answer. 283's are still all over the place and rebuildables can be had for $10 to $600. A running 283 could be from $10 to $1500. I've spent $600 for a numbers correct block before. Power pack head are out there and you will spend more on them than they are worth unless numbers matching is your game. How specific do you want to be with correctness when you place it in your truck? If numbers are not important, I would find a 350 (cheaper and easier to find and rebuild) and dress it up to look like it belongs there.

Here is a couple of blocks.

http://losangeles.craigslist.org/lac/pts/1503740963.html

http://inlandempire.craigslist.org/pts/1498230929.html

http://joplin.craigslist.org/pts/1492962928.html