Two ways to ask about price.
1. Noun + 多少钱duō shǎo qián + 一yī + measure word
e.g. 苹果多少钱一斤?
píng guǒ duō shǎo qián yì jīn?
How much is half a kilo of apples?
苹果五块一斤(Five yuan for half a kilo.)
píng guǒ wǔ kuài yì jīn .
菠萝多少钱一个?
bō luó duō shǎo qián yí gè ?
How much is for one pineapple?
菠萝十块一个。(Ten yuan each )
bō luó shí kuài yí gè 。
2. Noun+ 怎么卖zěn me mài?
e.g. 苹果怎么卖?(How much for the apple?)
píng guǒ zěn me mài ?