Would it be possible to add an option where it would cost say 250 scrap to spawn a mini?
Cost to Spawn Mini
Unlikely to be added. If implemented, then people will want to charge for a different item, them for multiple items, then for Economics or Server Rewards currency. Many plugins have already implemented those sorts of thing for shops. Reimplementing it in this plugin would be a waste of developer effort and bad for maintenance.
You can already integrate this plugin's API or server command with shop plugins to do this.
Vehicle license also support this if you want to use it instead.
Thank you for the info.