In 2006, LEGO released 3 Trains sets in the subtheme 9 V, all of these sets have been retired. For that year, the total price of all retail sets cost $165, today those sets are valued around $769, a growth of 366%.
Most valuable 2006 LEGO Trains set
10173 Holiday Train $614.32
3 sets

2159 9V Train Track Starter Collection

Theme / Subtheme Trains / 9V
Year 2006
Pieces 24
Availability Retired
2159 LEGO 9V Train Track Starter Collection
Retail $29.99
Value $58.46
Growth  +94.9%
Annual growth 2.8%

4206 9V Train Switching Track Collection

Theme / Subtheme Trains / 9V
Year 2006
Pieces 27
Availability Retired
4206 LEGO 9V Train Switching Track Collection
Retail $44.99
Value $96.11
Growth  +113.6%
Annual growth 4.2%

10173 Holiday Train

Theme / Subtheme Trains / 9V
Year 2006
Pieces / Minifigs 965 / 7
Availability Retired
10173 LEGO Holiday Train
Retail $89.99
Value $614.32
Growth  +582.7%
Annual growth 4.9%