when appraisal comes in below the selling price..

Just got appraisal report from my lender. It came about 30k (6%) below the sale price. The property is located in Brooklyn, where the bidding wars are very common this year. As I understand, the cases of lower appraisal happen often in a strong seller market. So what's the best course of action now? I plan to file a rebuttal on appraisal result to my current lender. In the meanwhile, I'd like to start 2nd mortgage application with another lender, hoping the appraisal report will come out more favorably. The worst case is that I just put extra 30k cash as down pay. Does this sound a sensible plan?