Fair prizes?(crown for cubes)

I participated in star crowns tournament
payed 750 cubes and won 3 crowns for second place.
First prize for that tournament is 5 crowns.

After the tournament I calculated the value of what I pay and the value of the prizes(if somebody decide to buy them).

The value of 750 cubes if I want to buy them seems to be 0.75$ based on 5$ for 5000 cubes.
The value of 5 crowns seems to be only 0.6$ based on 12$ for 100 crowns

I wonder if people who play in star crown tournaments(including the winners) do a bad deal or maybe it is not important because practically people cannot sell their cubes for crowns.

I thought about it and I think that generally crowns worth more than cubes because
I read that you can replace crowns with money when you cannot do it with cubes so I am going to play in tournaments that gives me prizes of crowns for cubes but not the opposite.

There is still one thing that I do not understand.

If the value of crown is 0.1$ and you can get 100$ for 1000 crowns then how it is possible that people can buy 500 crowns for 49$ based on what I read.

If this is correct then people can earn money without playing because they can buy 500,000 crowns for 49,000$ and later sell them to the site for 50,000$

Edit:I may decide to play in tournament that give cubes for crowns but not with the prizes that I see and the opportunity to win prizes like 250 cubes for 1 crown does not seem to me a good deal(If I am relatively good player I can win average of 3 crowns for 750 cubes in crown star tournaments so I can only get back my investment even if I win 250 cubes for one crown).