-Are these sentences grammatically correct and please let me know where I am wrong.
-Also any other better way to say these sentences.

Give me 1/2 kg potatoes.
How much are these potatoes for?
How are the potatoes ? (can we say this to ask price)
Has the price for tomatoes gone up.
Have vegetables become expensive?
Vegetables have become so expensive 1/2 kg for £10.

Give me half a kilogram of potatoes.
How much are these potatoes?
How much are the potatoes?
Have vegetables become expensive?
Onions/potatoes/rutabagas have become so expensive half a kilogram for £10.