Buying car from used car lot & if I pay it off in full in cash,how much of a % should I ask off on the price?

You should get the best price you can before HOW you are paying ever comes up. You don't usually get a discount for paying cash, in fact sometimes the dealer gets a bit less if you pay cash because he usually gets a little back from the finance company that takes your loan.

Hard to say.

But throw blue book value away. Nobody pays that.

Id say its probably a $1500-2200 wholesale piece.

You could probably get them down to a $1000-1200 deal if you negotiate well and be willing to walk. So...$2500-3400 max excluding tax & title.

This assumes an "as is" sale for cash.

Any warranty or buy here pay here jacks the price up a lot.

You're getting it hundreds of dollars less than what it's worth. The dealer and the salesperson have families to feed, mortgages to pay - don't be a cheap turd and try to weasel them down further.