Remember that the "su" of desu and desu-ka is actually pronounced dess and dess-ka.

We must also add a few words about price negotiation: With the exception of some parts of western Japan (particularly Osaka) it's not common to negotiate prices—or, for that matter, anything. You basically have a wide selection of whatever is in the standard set of options, but if you want something off-menu, it's going to get very complicated.

In fact, most staff will simply tell you they can't make an exception. This isn't because they don't want to please you, but because they likely don't have a rule for addressing the kind of request you're making. And if there's no rule, that staff member doesn't have the authority to make one up on the spot—it's something that probably has to involve everyone in the company from the top down.

That said, bazaar stalls and small shops along market streets will often be quite accustomed to negotiation (though not necessarily happy about it!), and you might be able to swing a deal at an electronics shop if you're able to engage in some back-and-forth.

Good luck and happy shopping!