The only problem with ranges is anchoring, particularly with dollars and cents. If I tell you it will be $1-10M, you're going to anchor on $1M (and be pissed when I come in at $8M).
(The reverse is true for, say, salaries. If you tell me you pay $100-$200k/yr for a job, I'm already thinking about how to spend that $200k.)
So your ranges should be within your negotiating contingency (say, 20%).
