Depends where you live and what the shops are like.
If your 24g protein from powder costs $1, that's $1/0.024kg = $42/kg protein
Here I can get
- topside steak, 1kg, $8 = 250g protein, $32/kg protein
- almonds, 1kg, $8 = 220g protein, $36/kg protein
- roasted peanuts, 1kg, $7 = 248g protein, $28kg/protein
- eggs, tray of 30, $6 = 195g protein, $31/kg protein
- UHT milk, $1.08/lt = 32g protein, $34/kg protein
- chicken breast, $8/kg = 300g protein, $27/kg
and so on - regular prices only, not specials.
The reason for protein and carbs powder is two. Firstly, if you find it physically difficult to eat the volume of food to give you enough carbs and protein. Secondly, if you need something which can digest very quickly, such as before or after a workout - regular food can take 2-6 hours to digest properly, a shake can be through you in half an hour.
But it ain't cheaper unless you're getting premium steak, salmon, or are generally very bad at shopping