Before you do anything, make sure you current setup is working to its fullest potential. Otherwise, you won't realize the full benefit of new cams, heads, intake, etc... The nice thing about the late 70 & early 80 GM's is that they have a considerable amount of potential for tuning.
First, address your timing. The mechanical advances in the '80 HEI's don't fully advance until 4600 RPM's (or something close to that). Re-curve your advance so you are "all-in" by about 3000 RPM and make sure your initial & total timing are correct. This should cost your less than $20 bucks if you have a plain-Jane timing light. You should notice a slight seat-of-pants improvement.
Second, address your fuel system. It is a 4 bbl Q-Jet, right? Make sure the idle air mixture is correct (limited adjustment on that year). Make sure the float levels are correct (ie. rebuild it). Have somebody hit the gas & make sure the primary & secondaries open fully (mine didn't on my 80!). Make sure your primary throttle shaft has no play, otherwise, have it bushed to cure the vacuum leak. Also, make sure the base plate is not warped. You may even find some benefits from slightly larger jets/rods. Check that your lines are not kinked, that your tank's pickup screen is clean (drop the tank - yuck), and that your pump is up to the task. Again, relatively cheap here.
Third, let your exhaust breath. Now you're spending a little money.
Then, change cams & intake. Now you're spending more money. The best bang for your buck would probably be to find some decent vortec's & a matching intake/cam. I hate to see people put fresh heads on an old bottom end though. You'll suck oil.
Good luck!