In a meeting held in Mojang, you have this:
https://account.mojang.com/documents/minecraft_eulaThe eula is a way not to rip off money off players. This was stated because of the many complaints mojang was recieving from Parent/Guardians saying, "200 for something" etc etc. With the eula system, this is a way so server can not rip off money from players.
e.g. $50 a month just for vip
If you would want to sell something, you would have to get permission from Mojang if it is legal. If you would not, servers would most likely get taken down immediately. Also, the pricing for servers have changed. With this, the price has now risen.
In a way, you can't sell kits/vip kits that expensive. If so, you would need to make sure that it is consistent with mojang's regulations.
This is only from my knowledge. Feel free to research more.
Some more information.
colindeng