From the owners and service manual.
The Moog Taurus II is a two-box pedal synth with a separate one-and-a-half octave pedalboard linked by a 5-pin DIN cable to a synth module. This module is essentially a Moog Rogue synth with a pedalboard controller. The synth module can be mounted on a metal tube (like a mic stand) which can be screwed into to the pedalboard, thus leaving the hands free to manipulate the parameters while your feet operate the keys.
Although they are rare, the originals are available from vintage synth dealers and occasionally from private sales and music stores. Primary factors in determining the price are the overall condition of the pedals, and whether or not the seller/store is aware of the current value in the vintage synth market. The Taurus IIs seem to be less sought after and appear relatively often in music stores that have a used synth section.
Over the last two years, the asking price of the original taurus pedals in private sales has risen from about $350 to around $500-600 for a set in good condition. I have seen them advertised for $850 and as high as $1100 (!). As for many fashionable vintage instruments, what an item is worth and what someone is prepared to pay for it are two different numbers. Most musicians I know who have a set have paid somewhere around $350, but have paid an additional price in time spent searching for a reasonably priced set.
The Taurus IIs appear to go for around $250 from stores; I bought mine, in bad condition, for $150.
Start with the obvious: Does every pot and slider work as it should. Do the presets work? Do the LED indicators for each preset work? Do the loundness and filter foot-controls work smoothly? Do the glide, octave and decay buttons work as they should?
Does the synth sound right? This can be a difficult test because the oscillators and presets go out of tune fairly quickly. Most likely, if the unit has been sitting in someones basement for a couple of years, it will sound dreadful. Whilst the front panel tuning knob adjusts the overal frequency up and down, the relative frequencies of the oscillators are adjusted by internal trimpots. My suggestion is to switch to the taurus preset, open up the unit and find the "taurus" trimpot. Then adjust this trimpot until the oscillators produce almost no-beats. If you do'nt hear some semblance of the classic taurus sound then there may be some internal problem requiring expert attention.
While you have the case open check to see if there is any evidence of internal modification. Common, and relatively harmless mods, are installation of the balanced output and the replacement of the trimpots (this was a factory suggested modification).
Very carefully check the pedalboard contacts and switches. The switches are often a problem area and are rather unique and consequently difficult to replace. Check for rust, dirt and general degridation and/or abuse of the contacts. Check that all the pedals work. If they do'nt then the contacts could need cleaning or realigning or it could signal a more serious problem: to be sure, perform a visual inspection of the contacts.
The original brown bakelite pedals corresponding to the "white" keys are quite fragile and it is unusual to find a set of pedals with these items intact. It's easy to make wooden replacements that are more durable. The best way to stop the plastic pedals breaking is to use the synth on a carpet.