Worth knowing how often no works, because the fear of losing the deal is usually larger than the risk.
In my experience most people who ask for a discount buy anyway when the answer is a polite no with a reason. They asked because asking is free.
What a good no sounds like:
Brief, warm, and not apologetic. We keep pricing the same for everybody, which is what lets me keep it where it is.
Offer the alternative in the same message, from the list above. A no plus an option is a negotiation; a bare no is a wall.
Do not explain your costs. It invites a discussion about whether your margins justify the price, which is not a conversation you want.
What to watch for: who is asking and why. A procurement department asking as policy is very different from a founder saying this is genuinely more than we can spend. The first wants a concession to report; a small trade satisfies it. The second is telling you something real about fit, and the honest answer might be a smaller package rather than the same thing cheaper.
And if they walk over twenty percent, you have learned something about how much they valued it - which is worth knowing before you build a relationship around them.