Why do you want to replace rockers and rings anyway? It might not be so serious. And if the rockers are making tapping sounds, you may also need valves, cam (ohc) and tappets. I had a tapping lifter (tappet) on an escort that was intermitant, (figired it was sticking) so I ran some "engine flush" once. It didn't fix it immediatley, but I just drove it and changed the oil regularly and it went away. Have over 220K on it now.
You might be able to buy just those parts for $400. But with any engine rebuild, you might as well replace some other parts while your in there. Your going to need to remove the heads to replace lifters and valves. And remove oil pan, to remove pistons to replace rings.
so you will also need
valve cover gaskets
Head gaskets
Oil pan gaskets
any other little intake gaskets
I would also replace
Rear & front main seals
may want to consider more depending on condition
oil pump
other seals and gaskets
rod bearings