Has this been made?? You can do commands to get different potions for different times. You can only use the potion effects command once every 5 minutes(after potion wears off) Permissions are needed for a user to use this command. This would be good for pvp servers, so players could buy the ability to get strength, etc. IF this has been made, link me. If not, then I will make it. I just need to know if it has been made or not. If you like this idea comment. I will be done tommorow if it has not been made
This doesn't do exactly do what you want, but it is the closest: http://dev.bukkit.org/server-mods/potioncommands/
http://dev.bukkit.org/server-mods/ntks-potions/ This is what he is currently developing. He will have cooldowns and prices very soon.
@Icpvp a plugin very similar to what you said is: http://dev.bukkit.org/server-mods/potionization/ the only problem is that you can't use potions on other players (until now)