We all like to eat out, it is a great reward for say a hard week of work, a celebration, etc. Restaurants have overhead, that is ok, there is expenses for the electric to run the fridges, freezers, dining room lights, etc, gas for the stoves and ovens, labor for the cooks, wait staff, and cleaning staff, cost of crockery, etc. But keep in mind, many common dishes are over priced for a reason, profit margin, and can be made for very little when prepared at home, but you have to be willing to cook, that is the key.
Bangers & Mash. Which I like, I can make 6 servings for the price of one serving in a low rent guest house restaurant, the prices in a high end restaurant, well, that is just a rip off. Low end places are using Thai sausage and more than likely instant mashed potatoes, the gravy is cheap. High end places are using the same Thai sausages and may make their own mashed potatoes, which is cheap but making a high profit on your account.
Fish & Chips. I can make a bucket of chips with a kilo of potatoes for less than the cost of the dish. Fish is Pangesius, about 180 Baht for 8 pieces. If cod, then that is a better, if stated as Dory, I would be cautious, I would even be cautious if the menu stated cod.
Meat Pies. I like meat pies but would never order one in a restaurant. Most places are using purchased pies from a number of manufacturers. I used to order dozens at a time as they are delivered frozen for 80-95 Baht each. The pie normally comes with mashed potatoes, may be instant or real mashed, either one is cheap.
Chili Con Carne. This is a money maker especially when served on rice, the rice is a filler. I make a large pot of chili when I make it, easily 12 servings, this is a over priced item.
Pasta. Anything with pasta is over priced in the low end places, the high end places that make there own pasta, good for them, and that warrants the price. Many Italian restaurants make their own pasta, which for that, would be worth the price charged, low end places, you can bet that is dry pasta from Makro. Same place I get mine!
Liver & Onions. I like liver, prefer mine with spicy mustard on the side, this is a very cheap meal to make, 250 grams of pork liver is 80 Baht (a serving would be about half of this), and a 1 kilo sack of onions is 28 Baht, the restaurant just made at least 100 Baht profit on you.
Cream of anything soup. You are paying at least double the cost of the can and only getting half the soup. Big profit for the restaurant. Canned cream of anything soups are mostly water and oil and flavored. Unless you make this at home, you are getting robbed by the store or a restaurant!
Tuna, Egg, Cheese, Ham and Cheese Sandwiches. Very over priced, I like all of these, I can make enough for several sandwiches then go out shopping or whatever, no need to pay 3-4 times the cost.
As I see more examples, I will post them here.