yup.. a good engine builder can do your existing engine ring and valves, new
oil pump, cam and timing chain for under a grand, maybe a little more if you need a crank, if you bring it to him. Tell him what you want and be flexible. Offer to help him (he most likely won't let you, but he might let you clean up the place) It might save you a few bucks.
If you really want to spend money, don't port and polish your heads replace them with edelbrock aluminum heads. They are $1200. but cheaper than porting and will give you more power. But now you are into $2500 for a very basic rebuild. 1976 390 heads are really restrictive and have huge chambers (low compression) If you don't feel like shelling out the $1200. Go with a set of say 1966-68 390 GT or IP heads, Much better flow and smaller chambers.. Good rebuilt heads like these are easily found for under $500. a pair.
If you want to do one thing aside from headers and a good intake get an MSD ignition, including the distributor. It will get you an extra 15 hp and get rid of a lot of problems you didn't even know you had. Of course that's another $500.