It is difficult to give an accurate value of anything but a Triola is
certainly a treasured item in mechanical music.  Here in Great Britain
I have seen them sell in specialist auctions at anything from GBP 600
to GBP 1900.  It all depends on the condition and the number of
potential buyers.

About ten years ago a well restored Triola appeared at a MBSGB
meeting and for the next few years the market price doubled.  Once all
interested parties had been satisfied, the price dropped once more.

The Triola is a tricky instrument to restore well and is also tricky
to play effectively, as it requires a musical input by the left hand,
in addition to turning the handle with the right.  It is, however,
well worth having one properly restored and taking the time to learn
to play it.  A well-played Triola will always get a round of applause.

Second-hand Triola rolls may be bought through mechanical music
society sales and specialist auctions (only very occasionally).
You may be able to obtain some modern rolls from Harald Mueller
<harald_m_mueller@gmx.de.geentroep> [delete ".geentroep" to reply]

Enjoy your Triola!

With best wishes from GB,
Nicholas Simons