[bbcbasic]

Tell them you earn $300k and have a $3M mortgage, and another offer.

Edit: Seriously though tell them it is none of their business and they should make an offer. If pushed then give them an amount that is at the very top end of your expectation. So if you are happy with $100k and wow for $120k then say you earning $140k and this just about covers your cost of living. If they ask how on earth you need $140k to live tell them that it is "for family reasons" and leave it at that.

If you already have given the number, just tell them you are finishing up an interview this week with another company. Then tell them you had an offer for $X. Then see if they increase their offer.