Young fella, I don't think anybody noticed the word "enexpensive" in your post. Unfortunately, horsepower is very expensive. If you have a very limited budget, the best horsepower gains would be in tuning and maintenance. First, give the engine a 100,000 mile tune up. PLugs, wires, K&N airfilter, a serious carb rebuild, good tires, brakes all around. New shocks and steering components. New hoses and V-belts.
First upgrade? A Pertronix ignition in your distributor. Second? 2" dual exhaust. Find a decent local exhaust shop and have them do it. Stay away from the big chains. As your budget grows, you can get into the more expensive stuff like heads, cams, intakes, headers, etc.
There is no one single upgrade that will make your car an instant boulevard screamer. The drivetrain works as a system that must be balanced to get full performance out any one upgrade. If all you did was to install a bigger cam, you wouldn't get your money's worth. It might even run slower.
Drive it stock and lay plans for a swap engine/trans.