$600 kit" consists of:

One Uni-Solar 32-watt amorphous-silicon PV module, 12 volts: $180.00

One Morningstar 6-amp charge controller, 12 volts: $40.00

Two Deka 92 amp-hour sealed batteries, 12 volts: ($130.00 each) $260.00

One Aims 800-watt modified sine wave inverter, 12 volts: $65.00

TOTAL: $545.00

This leaves you with $55 for wire, battery cables, mounting hardware, fuses between components, and the miscellaneous odds and ends that are always needed for any project of moderate complexity