Bukkit

I will like to charge = ($500+ (balance*0.10))

for access to a command I created, but not for use it. This means that I just want to charge once for them to be able to use it forever.
Do you know how can I do this or if I can even do it? :S

I actually want to charge for rent like want to give access to it for a week not forever but as far as I Know this is not possible.

This is the command
store:
command: /store
type: ALIAS
alias: /shop create 1 $arg1 0
permission-required: false
register: true
cost: 500+(/balance)*0.10

actually is this because I,m trying to hide the original because I don't know how to restrict te access to it u.u***

store:
command: /store
type: ALIAS
alias: /1/s*☻|♥1/s*|♥ create 1 $arg1 0
permission-required: false
register: true
cost: 500+(/balance)*0.10

Iguess I can ADD_PERMISSION but I dont know how to ADD_PERMISSION to a custom command that I'm creating, remember that I cant take permissions from the other one :S I.E I'm trying this, but obviously it will not work :S

addperm:
type: ADD_PERMISSION
text:
- '$6Add an extra permission to another existing command'
permission-node: mycommand.mybalance
register: true
permission-required: false
cost: 500

mybalance:
command: /mybalance
alias: /balance
permission-required: true
cost: 0


For your help
Thank you!

Use a perm system, like PermissionsX. When you user buy the option to use the command, the console perform the command from permissionX to add the perm to user. It works for me.