My parents retired and closed their shop last year....off my head, the prices were roughly....
Egg Fried Rice £3.20
Beef Chow Mein £6.50
Prawn balls £7
Customary free bag of Prawn Crackers (sold £2 separately)
You are not far off the £19. Part of the reason is the gas prices have shot up since the war started. Since takeaway uses gas (no other way to get the same heat), and in one those big burners not like your stove top at home. It gets expensive fast cooking even 1 dish, and the gas stays on all day, even during the day and between service on low (trickle mode). They use it more than just cooking when you order, some dishes needs prep during the day.
Raw materials have just gone up a lot, meat prices like beef have gone up. I used to be able to get a packet of mince in Sainsbury's for £1.59 for the 20% fat to make my burgers, the same packet is now £2.49. That's 90p more, like 50% extra now for the meat. This applies too for all the ingredients, minimum wage have gone up etc.
edit - If I were to get an order like the above...it's enough food to share between 2 people as 1 portion of the chow mein is more than enough for me in a meal. So throw in rice, chicken or prawn balls, that is enough food for 2.