Don't ask "what's your budget?". That's a spectacularly unsubtle way of asking what's the most you can shake someone for your product or service. A potential vendor asked me that a couple of days ago, and after that inauspicious beginning to our correspondence, he doesn't have my business and I don't want to deal with him.
Say what you think your product or service is worth, and justify it. Then we can negotiate and come to a price we both think is fair. It's not just about the money. The amount I'm up on my little anti-gold bet today is probably more than what that vendor was fishing for. There are enough a-holes in the world. You can differentiate yourself by not being one.