Depends on whether you genuinely feel that you're doing the right or wrong thing. If your financial position means you don't need the money, then get the camera and be honest about it. If you really should keep the money for more important things, do that.
Submitting to a nag is a bad thing, as it only encourages the behaviour. However, being an irresponsible partner is bad too, and you should just think clearly about what is happening here.