I think it's ok, but don't just tell them you want more money. Rather, explain to them that your experience is worth more than you are currently being compensated for. Then give supporting examples. In my opinion, that shows confidence in your skill set. I recently said this in an interview, of which I got the job. He then asked me why I chose their company (In other words, why not just try to advance in my current job.). To this, I replied that I felt their company provided more room for personal and professional growth, and offered more challenge.