When it comes to major mods, a couple hundred bucks is pretty much spare change.
There aren't alot of options anyway, maybe a better torque converter or valve box for the transmission, and going into the more expensive areas, new heads or a new, bigger engine, converting to MPFI. This is all $$$$ and more than a vanilla Chevy is worth. If you do start looking, I would suggest leaving the engine alone altogether, they're a decent engine, and instead upgrade the transmission. GM makes some decent engines, but then bogs them down with crappy transmissions and poor gearing. Do what you can to minimize the power loss between the engine and the wheels.