Further to your above post 30,000 to 40,000 Bht you suggest for 2 adults and a small child to live on would be a bit leans I live as a single mature male in a large condotel complex (34 s/m) in Cha-am about 25 km from Hue Hin...To get a reasonable town house to live in not far from the beach will cost about Bht 8,000/10,000 per month, quite nice+ 2.000 3,000 Bht for elect. and water, OK, but get a Thai Girl if possible to help you look, one with a bit of go she will get the correct price.
 You will need some kind of transport, second hand cars are expensive when compared to the West but very cheap to have maintained, so lots of old cars that are still good, new cars are sold in Thailand cost as much if not more then in the West, something to do with tax. Lots of cars are made in Thailand and exported to Australia and other places where they are cheaper.
The most common transport in your case if you live on your intended budget is 3 on a small motor scooter (I have a Honda click, 125cc auto) you with your tot between your knees and your lady "double dink" (Aussie term for passenger on a bike). Very common in all of S/E Asia and Thailand, not good but yes common and cheap. Hire a Scooter for about Bht 3000 p/m or you can buy good one second hand for about 20/25,000 bht pay no more.
Clothing , entertainment, and food yes could be managed very well if you eat mostly Thai food. Thai food is really very simple and is mostly made up of only a few basic combinations with sauces to taste, rice, veg small amounts of meat, fish poultry. The sauces can be mild, hot!, bloody hot! and F*** hot! and blow you head off hot F***, just like the weather in Australia. If you want to eat this hot stuff you will soon come like it, Thais have really destroyed their taste buds from early childhood and can eat things that can almost kill a westerner with this blow your head off stuff... Of course you don't have to eat all this hot stuff and stick mainly to Western food from Tesco, 7/11 and supermarkets but then you will be paying a lot more (that's me)...me yes but not always, don't let a Thai girl give you Thai food to test, they all double up laughing when they see how it affects farangs. When eating true Thai food and your a novice make sure you have a water bag, a bucket of water handy or a fire hose near by...you will need it.
All jokes aside, I think you your wife and tot could live OK in Hue Hin Cha-am or Patteya on a budget as you suggest. I am a mature aged male on a retirement visa but I make regular trips back to Aus for various reasons, not allowed to work (that's OK, I get the best of both worlds). I do have a better income then you but I'm still an Aussie Pensioner. The question for you depends on your age, if you need to work and how you would go about that "That is the question and the only question". If you can live on limited means and get a visa as required with all the requirements (THERE ARE LOTS) you will do OK in Thailand
PS... study up all the visa requirements online to see where you fit in, can be daunting. I or others on this site would enjoy seeing you succeed and giving to you the benefit of our experiences...best of luck?