Grab a core from your local salvage yard for $150-250. Then take it to your local machine shop. The shop that I use (which is an excellent shop) charges $632 to reman a shortblock and just over $800 for a longblock. That's with cast pistons and a stock cam, but hypereutectics are something like $30 more. You can buy your own cam as well. The stock cam costs something like $34, so they subtract $34 from the build and you buy whatever stick you want for about $120.
So, doing my math on the worst case scenario, lets say $250 for the core, $850 for the reman, $30 for better pistons, $100 for specific cam; that's $1230 plus tax. If you're "smart" you'll buy a vortec core that comes with the good heads. You'll spend more on the core and a few extra bucks on the build, but $1300-1400 should get the job done and get you 350 hp easy. Otherwise you might get terrible smog heads and end up with 250 hp. Starting with a vortec could basically mean 100 hp for $100 extra bucks.