In 2013, LEGO released 2 Power Functions sets in the subtheme Accessories, all of these sets have been retired. For that year, the total price of all retail sets cost $39, today those sets are valued around $123, a growth of 216%.
Most valuable 2013 LEGO Power Functions set
88004 Servo Motor $92.79
Largest 2013 LEGO Power Functions set
88003 L-Motor 1 pieces
2 sets

88003 L-Motor

Theme / Subtheme Power Functions / Accessories
Year 2013
Pieces 1
Availability Retired
88003 LEGO Power Functions L-Motor
Retail $13.99
Value $30.25
Growth  +116.2%
Annual growth 5.2%

88004 Servo Motor

Theme / Subtheme Power Functions / Accessories
Year 2013
Pieces 1
Availability Retired
88004 LEGO Power Functions Servo Motor
Retail $24.99
Value $92.79
Growth  +271.3%
Annual growth 11.4%