The player piano was just as popular in New Zealand as in most other countries during the heyday of the instrument (roughly 1905-1930). English, American, and Canadian-made instruments predominated, with the odd German player piano showing up as well.
Particularly popular brands in New Zealand were Barnard, Gulbransen, Gourlay, and Williams - all quality middle-range pianos - and even cheaper or lower grade brands from this era generally compare well to modern instruments of today due to the high quality of product back then and the fine materials used.
This is a popular question and the answer, sadly, is 'probably not much'. Although they are wonderful instruments capable of bringing an incredible level of interactive enjoyment into the home, the majority are also approaching 90 years old, and their satisfactory operation depends on complete airtightness of bellows and pneumatics covered with cloth, leather, and rubber. The quality of the music they produce is determined by valves operating to tolerances of thousands of an inch, and hundreds of moving parts - so as the difference between your grandmother's physical condition in 1925 and now, so it goes for the player piano.
Even if some degree of repair or restoration has been carried out over the years, it may very well have used inferior or incorrect materials and techniques. A perfectly restored player piano should be able to play easily, without undue effort, by gently pedalling with one foot. All the rapidly repeated notes so popular in piano rolls of the era should be able to play softly and evenly without any dropping out, and the music should be perfectly in rhythm, not jerky or stilted.
Another factor negatively affecting value is the change in musical taste over the years - modern music places much more importance on rhythm and beat than melody (with certain exceptions) and this doesn't transfer well to piano solo. And finally, of course, those who remember the player piano in its heyday are growing fewer and fewer.
A ballpark figure for a 'normal' brand player piano that has not had a professional restoration carried out on it would be between $150-$500 - and plenty fail to sell at that price for the simple reason they are big, bulky, heavy instruments that cost a lot to move and may not be particularly attractive if the case itself has not been refinished.
This doesn't apply to the magnificent reproducing pianos that are very rare in New Zealand - namely the Duo-Art, Ampico, or Welte. These will command much higher prices but are unlikely to be encountered.
Standard player piano rolls with brands such as QRS, Mastertouch, Broadway, 88 Note, may be worth between $1 - $5 each depending on titles and condition. The taste of modern collectors has tended to move away from the ballads, waltzes, and salon music that was so popular in the 'golden age' of player pianos, but the livelier fox trots, one-steps, and marches remain popular! Blues and rags from the 1900-1930 era command higher prices due to their relative scarcity.
My particular collecting focus is rolls branded 'RELIANCE', 'GOLDEN-TONE', and 'CELESTE-ART' - please contact me if you have any.
A full restoration to 'like new' condition will take months and cost in the region of $NZD6000 - $8000. This is for the player piano mechanism only, not the piano itself or case. Restoring the mechanism piece by piece is possible, as funds permit.
I would discourage an amateur 'handyman' from taking on a player piano as a project, due to the precision and accuracy required to get the player piano to play as it should - but if you must attempt it yourself or scrap the piano, please do borrow from your library Player Piano Servicing and Rebuilding by Arthur A. Reblitz - this is the 'Bible' of player piano restoration.
As some motivation - watch this video on Youtube to see just how human and beautiful a regular player piano can sound when restored to 'like new' condition.