nowhere near enough money.
steer clear of places like rai leh (riley) beach it is now a world class resort, used to piss cheap years ago but top dollar now,
on that budget you would have to stay somewhere cheaper like trang, get about on peds or songthaews, but that is best anyway as you can go different beaches each day, or take some trips inland
best to learn some basic thai before you go as you will get ripped off left right and centre to begin with, but you will still have an awesome time