You need a re-entry permit to allow you to travel freely in and out of the country. I believe it's 1k for the single and 3.9k for the multiple but I'm sure someone will be along shortly to confirm this.
may I suggest sticking to the 30 day extension first because if you want to extend again, you can the get the family 60 after the 30 but not the other way around. I'm sure
At Chang wattana they ask you to get it updated the day youngo back and pick up the final stamp so in effect making you leave the money in for 3 months. All offices have different rules though!