you can just keep coming back and forth with an entry stamp at the airport! If u try that at a land border you will only get 2 re-entry! If you have a visa or extension of stay you can get a re-entry permit all depends on what your status in Thailand is.
Phuket and Koh Samui are twice the price of Pattaya! Eating twice a day having good food is 800, 200 for coffee and breakfast, if u are staying in hotels gonna be 500 per night. 500 per day for incidentals. that 60k before you even have a beer! If u wanna stay in a shit hotel and eat street shit, stay home!
I suspect there is little point coming on an ED visa, it has been abused very much and I believe there are checks made on attendance and progress, if you really want to be a tourist, then be a tourist! Be aware Thailand is not cheap!
I would have all my ducks in a row before i tried to get any visa, so come to Thailand, sort things out, get an agent to help you, then come back to Thailand with plenty of money!