You currently have a share in the company which you want to sell. Without real revenue the company's value is almost entirely subjective. The right price then is basically what you can convince your partner to pay you for it.
If your partner calls your bluff and is prepared to scuttle the company that could well be $0. If (s)he believes in a bright future for the company it could just as well be $10+k though.
If you ever find yourself using those words when considering an action plan, run in the other direction as fast as you can. There lie antagonistic business practices. Ruining a friendship over a petty startup issues is not worth it. Nor losing your dignity. You're still friends, settle this as friends, each trying to make it beneficial to the other party.
The thing about a startup is that only the investors are really in a position to negotiate cleanly and with a clear head. If you're betting your time and effort, then by definition you're coming to the table with assets that are far more important to you than they will be to anyone else.
From my experience almost all cases where one party wants out and the other wants to continue (not just in tech) involve some amount of cash changing hands.
That amount being zero is just a special case for when very little value was accumulated. In that light giving "just walk away" as the general advice, even though it might be right in this case, is quite overly simplistic in my opinion.
And if your partner is also your friend you should also take that into account of course but from what I could tell the OP didn't mention anything about that.
Saying that the other party may 'call your bluff' implies that you're attempting to cheat them and hoping they won't notice. The word "bluff" is an euphemism for lies and deception. It's used positively in poker because the game rules allow it. But in real life "bluffing", i.e. deceiving and cheating, is frowned upon and often illegal.
The OP seems to have a relationship of trust with their partner and I'm urging him to keep it that way. I also meant it as a general business advice - it's important to keep friendly, trust-based relationships with people. Having to constantly look over your shoulder afraid of your co-founder stabbing you in the back, which is when phrase like "them calling your bluff" makes sense, is a lot of unnecessary trouble.
For me it was basically just a metaphor for negotiating over intangibles; without the apparent connotation of cheating your partner out of something.