Cams are short for camshafts. Camshafts open and close the valves that are in the head--they allow the motor to get air coming in and exhaust going out. Without going into too much detail so you don't get confused, duration and lift are often considered when planning to purchase cams.

By head work, I was referring to upgrading your valves and springs.

Your other option is to port and polish your intake manifold and have the head flow tested and ported and polished to match. This option is extremely expensive, and will overshoot your budget of $300 many times over.