Im just going to give you the experience on one we went to just the other day, but the prices and what kind of food is on offer depends from restaurant to restaurant. To add further more to this the restaurant we choose was the cheapest we have found so far in our area we are living . Some BBQ can be really deluxe and can be found in top hotels even in the Hilton corporation.
The Thai BBQ we went was an outdoor restaurant and cost 159 Baht per person for unlimited time (Some places do have a time limit and if you go over the allowed time, you will be charged extra depending on the rules of the particular establishment), with unlimited food and bottled water and there was also unlimited pepsi available but that was the one and only brand of soda they do.
What happens first is you get seated by the waiter/waitress to your own private table and a big ceramic pot is placed in front of you with burning coals in. you are given a stainless steel disc with a moat around the edges which you place on top of the ceramic pot and pour what is a clear soup into the moat. While you are waiting for this to heat up you can go and get your cooking ingredients to bring back to where you are sitting
There is so much food to select from various types of pork, chicken, shrimp, beef, squid just to name just a few raw meats with a big selection on vegetable, eggs and sushi. There is also a cooked section with chicken nuggets, french fries, sausage and other snack foods as we call them to enjoy while your waiting for raw meat to cook
Obviously this is the first stage of the buffet and doesn't look the most appetising but the more you grill and the juices drip into your own made soup the more colourful and tasty it is going to be. This is always a huge hit by the locals as its cheap, plentiful and its a great place to meet with friends to socialise. As you can see pretty much every table is taken here.
After you fill your boots up and are almost stuffed there is also a selection of fruit, jellies and ice cream (which we believe is the brand "Nestle Ice Cream") to finish off on and to end a nice evening with your family or friends before retiring home because you are too full to care and do anything else.
Now don't get us wrong, this is not the best quality buffets in Thailand you can find, but for the price its a steal, unlimited food which is fresh and tasty, unlimited bottled water and Pepsi and a deserts section for 159 Baht you can't grumble (they even had Thai football (soccer) on the television as well). Just one little note that most of these BBQ will charge you extra if you have leftover food on your table when you are about to leave, i can't give you a price as we had ate everything on our plates and left satisfied and happy on our dinner this evening.