I did my best to tweak the numbers you provided to come up with a good guess.
Price of loose packs: $12,000. Add a 15% premium for knowing your packs are unweighed if they come from a box + some people prefer to collect boxes = $13,800
PokeRev purchased box for $14,000: Subtract 2% due to sellers feeling more comfortable selling to an established buyer = $13,720
PokeRev selling packs for $15.3k: Subtract 5% due to his reputation from other box breaks, others might not be able to command the same premium = $14,535
DA card world selling for $15,000: Subtract 3% for store overhead costs = $14,550
One currently on eBay from Crash Cromics for $14,000: Add 3% store fees but subtract 2% for eBay buyer protection benefit so just add 1% = $14,140
So in total we are looking at a range of:
$13,720 - $13,800 - $14,140 - $14,535 - $14,550
This gives you an average of $70,745 / 5 = $14,149
However the cheapest and most expensive may be outliers so without them the average is $42,475 / 3 = $14,158
As a buyer I would try to find a box roughly between $14,149 and $14,158. Of course if you find a case fresh one that can add a few % points to the value.