The stage 2 of Vila Sale offers 16*12 hour boosts. One 12 hour boost is approx 150 crowns i.e. 16*150(=2400) crowns worth of boosts.
This costs me 1300 of my currency. So basically cost of per 100 crown is 1300/2400*100(=54.16)
Then I have "just for you" offers: 5850 crowns in 1950. Cost of 100 crowns is 1950/5850*100(=33.33).
The normal values of crowns is: 14000 crows in 6400. Cost of 100 crowns is 6400/14000*10(=45.71)
So basically speed ups are Nexon's way of handling inflation/price hike(or a new way to do mathematics).
Either way, it looks like it is not a company that cares much about customer experience.