The lowest cost Z METER is a bass audio sine wave generator (15 to 150 HZ). If you have a multi-meter with the HZ meter function this is the least expensive version but does not include the impedance bridge circuitry. It requires a 12vdc power source less than 1/4 amp.
ONLY $89

The upgrade to the basic bass audio sine generator
Z METER includes the digital HZ METER DISPLAY. The accuracy is +/- 1% and reads to the nearest tenth of a cycle or hz.
ONLY $169

Here is the full version of the Z METER with digital HZ readout, bass audio sine generator, and the impedance bridge that measures you speaker impedance (actively at 15 to 150 HZ) from 1/4 to 119 ohms.
ONLY $199