Legendary's started in 2012. I have averaged the quantity of the trade goods so with only one 2013 legendary it may be an abnormality (also excluded CoA). Here is what I found.
- UR started to become a part of the recipe in 2014 (with 1 recipe requiring it), and starting in 2015 they almost always needed 2 UR. This is an increase in the Legendary cost.
- Golden Fleeces were always required but staring in 2018 the requirement moved up to 2.
- Aragonite has sleadly increased and is now up to an average of 4
The average's (not counting 2019) for the following trade goods are:
Alchemists Ink - 5.0 (2019 draft is 10)
Alchemists Parchment - 11.7 (2019 draft is 6)
Aragonite - 2.8 (2019 draft is 2)
Darkwood Plank - 13.8 (2019 draft is 18.3)
Dwarven Steel - 14.7 (2019 draft is 8)
Elven Bismuth - 2.3 (2019 draft is 2)
Enchanters Munition - 3.8 (2019 draft is 8.3)
Golden Fleece - 1.1 (2019 draft is 2)
Minotaur Hide - 6.0 (2019 draft is 2)
Mystic Silk - 14.9 (2019 draft is 16.7)
Oil of Enchantment - 2.3 (2019 draft is 2.0)
Philosphers Stone - 8.2 (2019 draft is 15)
Conclusion
2019 is above average in AI (5), DP (4.5), EM (4.5), MS (1.8), and PS (6.8)
2019 is average on Golden Fleece with the increase last year and UR with the increase in 2015
2019 is below average on AP (5.7), Aragonite (.8 but really more), DS (6.7), EB (0.3), MH (4), OE (0.3)
Seems inline with average legendary costs.
Ed