Col
TY250 twinshocks are popular in Classic Trials competition so it would have value to people who want to ride one in Trials. By 1977 the TY250 had been rendered old hat by more modern designs by other manufacturers, but they were still being sold (mainly to trail riders).
All the TY 250 twinshocks are mechanically similar ie easy interchangability of parts. The B,C,D and E models are slightly better for competition use than the first TY250(A).
TY250 twinshocks are extremely common so condition is the arbiter for price.
The model with the white tank and red stripe as standard is the D model that first came out in 1977 but sold for a few years. It should have motor and frame numbers that go 493-20xxxxxx.
Most D models sold in OZ were pale blue with "feathers" on the tank - a bit hippy looking for some. In Europe and Canada they decorated them more plainly with the white and red.
David