How to say how much is this in Hindi
One question does most of the work in a shop, and it has a small catch: the ending changes depending on what you are pointing at.
The question
का, की and के agree with the item, not with you. कुर्ता (kurtaa) is masculine, so कितने का. साड़ी (saaRee) is feminine, so कितने की. If you have no idea which one a thing is, point and say कितने का, and nobody will stop the sale over it.
Simpler versions when you are stuck
Bargaining
Bargaining is normal in a market and not done in a shop with printed price tags. The tone is friendly, not adversarial. रहने दीजिए said while turning away is the oldest move there is.
Choosing and paying
The grammar worth keeping
मुझे यह चाहिए has no "I" in it. Wanting, needing, liking and knowing all put the person in the मुझे slot and let the thing be the subject. It is the single most useful pattern in the language: मुझे पानी चाहिए, मुझे चाय पसंद है, मुझे हिंदी आती है.