Hi, I really suggest you rent, at least at first - there are many reasons for this including the fact that as a foreigner you can't legally own land anyway.
Rents can go from 6k skywards. For a nice 2 bed house (not condo) in my part of town (Chaing Mai) you coul easily get away with 8-10k these days. I have a 4 bed +maids room, 3 bathrooms, fully furnished with front and back gardens for 18k/month. I am not sure about K. Samui, bt it will be more expensive as there are more people per Km and its a tourist/holiday home area.
Electricity depends on how many aircons you have and how often you use them. I have 4, but only use 2 to 3 overnight - the other is in the spare room and unused most of the year. I also have several TVs and computers that seem to be on far too often. In all I pay around 1,300B/month.
For internet I pay for MaxNet premium (4Mb) and dedicated line and it costs me a cool 1,200/month.
Gas comes in a bottle and I have never had to refill it yet, so not sure of the price.
Food shopping I spend around 5k a month (4 of us).
Going out, treating the kids, petrol and sundries I probably spend another 5-10k/month give or take.
Car tax is about 1,200B/year.
Health insurance is about 35k/year (3 of us).
If you have kids then schooling will probably be the most expensive thing you pay for.
I have never paid a bean in local taxes (don't know if my rent incluides this - or it doesn't exists) - but my bin is emptied every night (except Sunday) and the streets are kept clean.
If you live on a mood Bahn (like a Spanish urbanisation or a gated community) you will have other costs like maintance fees, club membershp, security fees etc - I don't.
Don't forget import taxes on anything you ship (first shipment is somewhat tax free - after a fashion - depending on what is in it) if you have a non-tourist long stay visa. After that its extortionate. Animals are charged import tax regardless (if cargo shipped). Put your Xbox in your hand luggage and carry itover - I did
Good luck.