In 1966, LEGO released 12 Trains 4.5V sets, all of these sets have been retired. For that year, the total price of all retail sets cost $79, today those sets are valued around $5,681.
Most valuable 1966 LEGO Trains 4.5V set
113-2 Motorized Train Set $3,761.41
Most owned 1966 Trains 4.5V set
150 Straight Track
12 sets

100 4.5V Motor with Wheels Small

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 16
Availability Retired
100 LEGO Trains 4.5V Motor with Wheels Small
Retail $5.99
Value $188.85
Growth  +3052.8%
Annual growth 5.9%

100-2 4.5V Motor with Wheels Large

Theme / Subtheme Trains / 4.5V
Year 1966
Availability Retired
100-2 LEGO Trains 4.5V Motor with Wheels Large
Retail $6.50
Value $191.72
Growth  +2849.5%
Annual growth 5.8%

101-3 4.5V Battery Case

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 1
Availability Retired
101-3 LEGO Trains 4.5V Battery Case
Retail $2.35
Value $40.92
Growth  +1641.3%
Annual growth 4.9%

111-2 Starter Train Set without Motor

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 123
Availability Retired
111-2 LEGO Starter Train Set without Motor
Retail $6.95
Value $174.99
Growth  +2417.8%
Annual growth 6.3%

112-2 Locomotive with Motor

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 76
Availability Retired
112-2 LEGO Trains Locomotive with Motor
Retail $7.25
Value $702.05
Growth  +9583.4%
Annual growth 7.9%

113-2 Motorized Train Set

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 402
Availability Retired
113-2 LEGO Motorized Train Set
Retail $16.99
Value $3,761.41
Growth  +22039.0%
Annual growth 9.4%

114-2 Small Train Set

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 88
Availability Retired
114-2 LEGO Small Train Set
Retail $4.25
Value $510.22
Growth  +11905.2%
Annual growth 8.3%

115-2 Starter Train Set with Motor

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 139
Availability Retired
115-2 LEGO Starter Train Set with Motor
Retail $22.00

150 Straight Track

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 28
Availability Retired
150 LEGO Trains Straight Track
Retail $1.50
Value $22.51
Growth  +1400.7%
Annual growth 4.6%

151 Curved Track

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 28
Availability Retired
151 LEGO Trains Curved Track
Retail $1.50
Value $21.88
Growth  +1358.7%
Annual growth 12.3%

152 Two Train Wagons

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 28
Availability Retired
152 LEGO Two Train Wagons
Retail $2.10
Value $31.12
Growth  +1381.9%
Annual growth 4.6%

153 Large Train Wagon

Theme / Subtheme Trains / 4.5V
Year 1966
Pieces 18
Availability Retired
153 LEGO Large Train Wagon
Retail $2.10
Value $35.16
Growth  +1574.3%
Annual growth 5.5%