Don't invest too much time in thinking about the zillow website. It is widely known to be far off much of the time. I personally wouldn't want to pay for 2 appraisals. Just go forward with the refi, most of the closing costs occur after the appraisal anyway so it is not like you're are locking yourself into a bunch of expense at the risk of not getting rid of PMI.

Also getting two appraisers can be pretty far off from each other, pretty hard to tell when going into a refinance where you are going to land. I would just spend 30 minutes studying per square foot selling prices for condos in the same area that have the same # of bedrooms and are on the same floor if you want to get a general idea before getting started.