Going back to what Bob said, before you even consider uping the HP on your car, at a minimum inspect the steering, brakes and tires. If any of these are marginal spend you money there FIRST.

On your $700 budget, I would start hunting for a decent running small block V8. If you can find a complete one for a decent price (or a complete donner car), you should be able to squeek by with the rest of the parts you need;

V8 motor mounts
Bigger radiator
Special oil pan and pickup (this is a must as the stock chevy pans will intefer with the steering).
Exhaust

It's doable, but you will need to do a lot of smart shopping.