I Am Buying a Car. The seller is asking for $8000. I want to ask to him if he could give it to me for less then that price. How many possible ways to say this in American English? Please make corrections to my grammar usage above.

You could say:
"Do you think you could come down a little on the price?"
"I'm not sure the car is worth $8000."

You could suggest a lower price:
"Well, how does $7000 cash sound?"
"Would you consider taking $7000?"
"How about $7000?"

If the car has a problem, you could mention it in your negotiation:
"I'll have to get the brakes fixed, so I really don't see paying more than $7000."
"Since the car has so many miles on it, maybe we can negotiate a lower price."

"How many possible ways are there to say this in American English?"
"...for less than that price."

By the way, if you're planning on driving the car for over a year or two, don't buy an American car. The money you save will be eaten up by expensive repairs to tiny components.