The royal crystal to blue crystal rate appears to be set by Smilegate.
Under the description at the currency vendor, it states "Crystals are traded by the hundred with a set rate of 100 crystals = 238 royal crystals"
USD
Royal Crystals
This should be based on whatever shop rate you pick.
$9.99 is 1,000 Royal Crystals
$19.99 is 2,220 Royal Crystals
$49.99 is 5,750 Royal Crystals
$99.99 is 12,000 Royal Crystals
Royal Crystals
Gold
Royal crystals to gold is based on market rates on each server.
Gold
Blue Crystals
Gold to blue crystals is based on market rates on each server.
1 currency to all others
From currency
Amount
Gold
Blue Crystals
Royal Crystals
USD
Converter and Outputs
From Currency
Amount
To Currency
Amount
Comment
Royal Crystals
To Gold, then Blue
This may seem silly, but it's assurance that buying blue crystals directly in the shop is a better deal. Efficient markets etc etc.
Blue Crystals
USD
This helps understand how much something in Mari's shop is really worth.
Gold
from Royals from USD
How much is gold worth in USD? Helps to understand real item value.