Another inexpensive one is to switch from the stock 1.5:1 ratio rockers to the 1.6:1.
This adds lift to the valves which gives the same results as a mild cam changeout...without changing the cam. You would see a noticeable improvement in your low end torque and response straight away.
Ideally the rockers would be roller or equivalent...and you might get a good deal locally (used) or thereabouts.
Coley