How much do you pay for it?
How much you pay/paid for it?
What's the difference between the two ?
How much do you pay for it?
How much you pay/paid for it?
What's the difference between the two ?
How much do you pay for it? is grammatically correct, though you'd rather say How much did you pay for it? as it refers to an action that obviously happened in the past.
How much you pay/paid is not grammatical unless used as a question word clause like Tell me how much you paid for it.