My appraiser says he believes his appraisal and my ex's will be very similar, and that the cost of the appraisal may not be worth it. I need help with this math.

I bought my home two years ago for $320k. I owe $288k. If my ex's appraisal comes back at $330k, and my appraiser was correct in saying his will be within 5% of the other guy (Because he knows the other guy and believes they will be similar,) 5% of $330k is still $16.5k. The cost of the appraisal is $500. If the difference is 16k, and the judge averages the two, the difference becomes 8k, which we split. Her equity goes down by $4k.

For example, Hers is $330k, mine is 5% less at $313.5k. the value averages at $321.75. Less the amount owed is $33.75k. Split 50/50, she gets $16.9k.

Not getting mine done and going with hers raises that $16.9k to $21k.

Theoretically, the difference would only need to be $2,000 between the appraisals for me to get the cost of the appraisal back, right? The appraisals would need to be within .6% of each other for the cost to not have been worth it. That seems highly improbable to me. Is a $500 payment for a one-in-ten chance at $4000 worth it?